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In any one grain they are piled with perfect regularity, These are now familiar facts. Can we attempt to explain all facing one way, like a regiment of perfectly similar them on the basis of a molecular theory which will at the wldiers formed up in rows, where each man is equidistant same time offer a clue to the process of crystal-building from his neighbours, before and behind, as well as to right as we find it in metals? I venture to make this Address and to left. Or perhaps I might compare them to the well- the occasion of inviting attention to some more or less drilled flowers of an early Victorian wall-paper.

speculative considerations which may be held to go some It was shown by Mr. Rosenhain and myself that when little way towards furnishing the material for such an a piece of metal is strained beyond its limit of elasticity, explanation. so that permanent set is produced, the yielding takes place At the Leeds Meeting of this Association, in 1890, it was by means of slips between one and another portion of each my privilege to bring forward certain contributions to the Crystal grain. A part of each crystal slides over another molecular theory of magnetism, and to show a model which part of the same crystal, as you might slide the cards in demonstrated that the rather complex phenomena of a pack. It is as if all the soldiers to one side of a given magnetisation were explainable on the very simple assumpline were to take a step forward, those on the other side tion that the magnetic molecules are constrained by no remaining as they were, or as if all the men in the front other forces than those which they mutually exert on one Tows took a step to the left, while those in the rows behind another in consequence of their polarities. From this hept their places. In other words, the plasticity which a were found to result all the chief phenomena of permeability inetal possesses is due to the possibility of shear on certain and magnetic hysteresis. Let us attempt to-day to apply planes in the crystal that are called “cleavage considerations of a similar character to another group of " gliding " planes. Plastic yielding is due to the occurrence physical facts, namely, those that are associated with the of this shear; it may take place in three or more direc-crystalline structure of metals and with the manner of tions in a single grain, corresponding to the various their yielding under strain. Just as in dealing with magpossible planes of cleavage, and in each direction it may netic phenomena, 1 take as starting-point the idea that the isappen on few or many parallel planes, according to the stability of the structure is due to mutual forces exerted extent of the strain to which the piece is subjected. on one another by its elementary parts or molecules, and Examine under the microscope the polished surface of a that the clue to the phenomena is to be sought in the piece of metal which has been somewhat severely strained play of these mutual forces when displacement of the after polishing, and you find that the occurrence of this molecules occurs. shear or slip is manifested on the polished surface by the Iron and most of the useful metals crystallise in the appearance of little steps, which show themselves as lines cubic system ; for simplicity we may limit what has to be or narrow bands when looked at from above. To these said to them. Imagine a molecule possessing polarity wr gave the name of slip-bands. Just as the piece of equally in three directions, defined by rectangular axes. metal is an aggregate of crystal grains, the change of We need not for the present purpose inquire to what the shape which is imposed upon it in straining is an aggregate polarity along the axes is due; it will suffice to assume effect of the multitude of little slips which occur in the that the molecule has six poles, three positive and three grains of which it is made up. Each grain, of course, negative, and that these repel the like and attract the unalters its form in the process.

like poles of other molecules. We may make a model by Speaking broadly, this distortion of the form of any one using three magnetised rods fixed at right angles to one Crain by means of slips leaves it still a crystal.

another at their middle points. I imagine, further, that of the group of brickbats moves forward, keeping parallel the molecule has an envelope in the shape of a sphere, 10 themselves and to the others, the formation remains which touches the spherical envelopes of its neighbours, regular, except that a step is formed on the outermost and assume that these spheres may turn on one another rows; the orientation of the elements continues the same without friction." throughout. Considerations which I shall mention presently Think now of the process of crystal-building with lead to some qualification of this statement.

I now

supply of such spherical molecules for brickbats. Starting rrason to believe that in the process of slip there is a with one molecule, let a second be brought up to it and disturbance of the elementary portions or brickbats adjoin- allowed to take up its place under the action of the polar ing the plane of slip, which may alter their setting, and forces. It will have a position of stability when a positive thereby introduce to a small extent some local departure pole in molecule A touches (or lies in juxtaposition to) a from the perfectly homogeneous orientation which is the negative pole in molecule B, with the corresponding axes characteristic of the true crystal. In very severe straining in line, and when the further condition is satisfied that there may even be a wide departure from true crystalline the axes in molecule B the poles of which are not touched character. We shall recur to this later; but meanwhile it by A are stably situated with respect to the field of force will suffice to say that substantially the slip which is exerted by the poles of A. involved in a plastic strain of moderate amount is a bodily In other words, we have this formation :translation, parallel to themselves, of part of the group of elementary brickbats or molecules which build up the

A grain. If a crystal the form of which has been altered, even largely, by such straining is cut and polished and etched it appears, under the microscope, to be to all intents and purposes as regular in the tactical grouping of its elements as any other crystal.

N S

S S/ Further, in the process of straining we have, first, an

W

N plastic stage, extending through very small movements, in

S which there is no dissipation of energy and no permanent set. When this is exceeded, the slip occurs suddenly; the work done in straining is dissipated ; if the straining force is removed a strain persists, forming a permanent "set"; if it continues to act it goes on (w hin certain limits) producing augmented strain. In general a large amount of For convenience of representation in the diagram the poles strain may take place without the cohesion between the are distinguished by the letters N. and S., but it must gliding surfaces being destroyed. Immediately after the not be assumed that the polarities with which we are here strain has occurred there is marked fatigue, showing itself concerned have anything to do with magnetism. in a loss of perfect elasticity: but this will disappear with Suppose, now, that the crystal is built up by the arrival the lapse of time, and the piece will then be harder than of other molecules, each of which in its turn assumes the at first. II, on the other hand, a process of alternate position of maximum stability consistent with formation in straining back and forth be many times repeated, the piece breaks.

1 “Contributions to the Molecular Theory of Induced Magnetism,"

Proc. Roy. Soc., vol. xlviii., June 19, 1890, or Phil. lag., September, 1890. | Ewing and Rosenhain, “The Crystalline Structure of Metals," 2 Or, let the envelope be a shell of any form, inside of which the axes Bakerian Lecture, Phil. Trans. Rey. Soc., vol. cxciii. A, 1899.

of polarity are free to turn as a rigid system.

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cubic or normal piling. The group in that case takes an kind, possessing little stability, may be formed during the arrangement which is essentially a repetition of this process of crystallisation, so that here and there in the quartette :

grain we may have a tiny patch of dissenters keeping one

another in countenance, but out of complete harmony with S

thrir environment.

If this happens at all during crystallisation, it would

seem less likely to happen in free crystallisation from a N S

S S
N

liquid state than in the more constrained process that occurs IN

when a metal already in the solid state recrystallises at a S

temperature far below its melting-point. Though rare or

absent in the first case, it might occur frequently in the 'N S

second. There are differences in the appearance of crysta! grains under the microscope in metal as cast and in metal

as recrystallised in the solid state, of which this may be S S IS N

N

the explanation. It may also explain a difference pointed

out by Rosenhain,' that the slip lines in cast metal are S UN

straight and regular, whereas in wrought iron and other metals which have recrystallised in the solid they rarely

take a straight course across the crystal, but proceed in Along each row the polarity preserves the same direction, jagged, irregular steps. These may be due to the presence but the polarity of each row is opposite to that of each

here and there of small planes of weakness, resulting from contiguous parallel row. This description applies equally

the existence of what I have called dissenting groups. to all three axes. The whole group (Fig. 3) consists of

Again, these groups, possessing, as they do, less stability the quartettes of Fig. 2 piled alongside of and also on top

than their normal neighbours, may be conjectured to differ of one another. In this way we arrive at what I take to

from the normal parts of the grain in respect of electrobe the simplest possible type of cubic crystal.

lytic quality, and to be more readily attached by an etchIn this grouping each molecule has the alignment giving

ing reagent. Hence, perhaps, the conspicuous isolated maximum stability, and it seems fair to assume that it geometrical pits that appear on etching a polished surface will take that alignment when the crystal grain is formed

of wrought iron. under conditions of complete freedom, as in solidifying from

It will help in making clear these points, and others the liquid state. As a rule, the actual process of crystal, by grouping a number of polarised "molecules.” in one

that are to follow, if we study the action of a model formed building goes on dendritically; branches shoot out, and from them other branches proceed at right angles, leaving plane, supporting them on fixed centres, about which they interstices to be filled in later. We have, therefore, to

are free to turn. In the model before you the centres are conceive of the molecules as piling themselves preferably uniformly spaced in rectangular rows, and the "molein rows rather than in blocks, though ultimately the block

cules” are + shaped pieces of hardened steel, strongly form is arrived at. In this position of maximum stability magnetised along each of the crossed axes, each having. each molecule has its six poles touching poles of contrary therefore, two north poles and two south poles. The third name.

axis is omitted in the model, the movement to be studied Now comes a point of particular importance. Imagine On placing these “ molecules" on their centres they readily

with the help of the model being movement in one plane. two neighbouring molecules in the same block to be turned round, each through one right angle, in opposite senses.

take up the position already indicated in Fig. 3. Each one They will now each have five poles touching five poles of

within the group has its four poles in close proximity to contrary name, but the sixth pole will touch a pole of

four poles of contrary name, and is, therefore, highly the same name as itself. They are still stably situated,

stable. If disturbed by being turned through a small angle. but much less stably than in the original configuration,

and let go, it swings back, transmitting a wave of vibraand they will revert to that configuration if set swinging

tion through the group, which is reflected from the edges, through an angle sufficient to exceed the limited range

and is finally damped out in the model by pivot friction within which they are stable in the new position.

and air friction. We may assume some damping action Similarly we may imagine a group of three, four, or

(say by the induction of eddy-currents) in the actual solid, more molecules, each to be turned through a right angle,

of which the model may be taken as a very crude reprethereby constituting a small group with more stability, but always with less than would be found if the

By turning two molecules carefully round together, each normal configuration had been preserved. The little

through one right angle in opposite senses, we set up a

group in question may be made up of molecules in a row, or it dissenting pair, the equilibrium of which has feeble stability.

A slight displacement, such as might be produced by the transmission of a vibrational wave, breaks them up, and they swing back to the normal configuration, giving out energy, which is taken up by the rest and is ultimately dissipated. By making the dissenting coterie consist of three or more we can give it additional strength.

An example is shown in Fig. 4, where the three molecules marked a, b, and c are turned round in this way.

Notice that the normal molecule d, adjoining a line ni such dissenters, is in a peculiar position. His neighbours present to him three N. poles and one S. pole. He has the choice of conforming to the majority, or of throwing in his lot with the dissenters; and he has a third possible position of equilibrium (very feeble equilibrium) which is reached when his two S. poles are turned until the en neighbouring south pole faces just between them. I have laboured these points a little because they seem important when we come to speak of the effects of strain.

Consider now the straining action, which we may imitate

in the model by sliding one part of the group past the may be a quartette or block, or take such a form as a other part. For this purpose the centres are cemented to Tor L. A sufficient disturbance tends to resolve it into two glass plates which can slide parallel to one of the agreement with the normal tactics of the molecules which build up the rest of the grain. It is conjecturally possible that small groups of this

1 Rocenhain. "The Plastic Yielding of Iron and Steel," Jour. Irmaet

Steri Institute, No. i for 1904, p. 335.

or less sentation.

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At first, when the displacement by sliding is exceedingly through the action of the molecular movements that are small, the strain is a purely elastic one. The molecules associated with heat, and hence the slow progressive readjacent to the plane of sliding pull one another round a covery of perfect, or nearly perfect, elasticity shown by little, but without breaking bonds, and if in this stage the the experiments of Muir. Let the temperature be raised strain is reinoved, by letting the plate slide back to its and they disappear much more quickly ; in warm surroundoriginal position, there is no dissipation of energy. The ings the rest-cure for elastic fatigue does not need to be work done in displacing the molecules is recovered in the nearly so long. return movement. We have here a representation of what Rosenhain ? has recently shown that after the slip-bands happens between each pair of adjoining rows in the elastic on the surface of an overstrained specimen have been straining of a metal. So far the action is within the limit obliterated by polishing, traces of them will reappear on of elasticity; it leaves no permanent effect : it is completely etching if only a short interval of time is allowed to lapse reversible.

since the overstraining ; but if time is given for complete But now let the process of straining be carried further. recovery no

are found. This is in remarkable The opposing molecules try to preserve their rows intact, agreement with the view now put forward, that the layers but a stage is reached when their resistance is overcome ; contiguous to the surface of slip contain for a time comthe bonds are broken, and they swing back, unable to paratively unstable groups. They are consequently different exert further opposition to the slip. The limit of elasticity from the normal metal until the unstable groups are has now been passed. Energy is dissipated; set has been resolved, and the temporary difference manifests itself on produced ; the action is now no longer reversible. The etching, provided that is done while the difference still model shows well the general disturbance that is set up in exists. molecules adjoining the plane of slip, which we may take From the engineer's point of view a much more important to account for the work that is expended in a metal in matter than this fatigue of elasticity is the fatigue of producing plastic strain.

strength that causes fracture when a straining action is Moreover, when the slip on any plane stops and the very frequently repeated. Experiments which I made with molecules settle down again, the chances are much against Mr. Humfrey: showed that this action begins with nothing their all taking up the normal orientation which they had more or less than slight slip on surfaces where the strain before the disturbance. What I have called dissenting is locally sufficient to exceed the limit of elasticity. An groups or unstable coteries are formed as a result of the alternating stress, which makes the surfaces slip backdisturbance.. Here and there like poles are found in juxta-wards and forwards many thousands, or it may be millions position. Viewed as a whole, the molecular constitution of times alternately, produces an effect which is seen on of the metal in the region adjacent to the plane of slip the polished surface as a development of the slip lines into

actual cracks, and this soon leads to rupture.

We have, therefore, to look for an effect equivalent to an interruption of continuity across part or the whole of a surface of slip, an effect progressive in its character, becoming important after a few rubbings to and fro if the movement is violent, but only after very many rubbings if the movement is slight.

That there is a progressive action which spreads more or less into the substance of the grain on each side of the original surface of slip was clearly seen in the experiments referred to. It was found that a slip-band visible on the polished surface of the piece broadened out from a sharply defined line into a comparatively wide band with hazy edges, and this was traced to an actual heaping up of material on each side of the step which constituted the original line.

I think this suggests that under alternating stresses which cause repeated backward and forward slips, these do not occur strictly on the same surface in the successive

repetitions, and hence the disturbance spreads to is now uncertain and patchy. It includes parts the stability surface leaves a more or less defective alignment of the

extent laterally. It may be conjectured that slip on any of which is much less than normal. Individual molecules or small groups in it are very feebly stable; a touch would

molecular centres; that is to say, the rows on one side make them tumble into positions of greater stability.

of the plane of slip cease to lie strictly in line with those Observe how all this agrees with what we know about

on the other side. If this occurs over neighbouring surthe nature of plastic strain through experiments on iron

faces, as a result of slips or a number of parallel planes or other metals. Its beginning is characteristically jerky. region loses its strictly crystalline character, and with it

very close together, the metal throughout the affected Once the critical force is reached, which is enough to start it, there is a big yield, which will not be stopped even

loses the cohesion which is due to strict alignment. by reducing the amount of the straining force.

Mr. G. T. Beilby, in a very suggestive paper,' has Again, we know that there is a slow creeping action that

advanced grounds for believing that portions of a metal continues after the straining force has done its main work.

may pass from a crystalline to an amorphous formation I ascribe this to the gradual breaking up of the more

under the mechanical influence of severe strain, as in the unstable groups which have been formed during the sub

hammering of gold leaf or the drawing of wire, and that sidence of disturbance in the earlier stage of the slip.

this occurs in the polishing of a metallic surface, and also Further, know that overstrained iron

in the internal rubbing which takes place at a surface of imperfectly elastic until it has had a long rest, or until slip within the grain. In both cases he suggests the formit has been raised for a short time to a temperature such

ation of an altered laver. When a polished metal surface as that of boiling water.' This is to be expected when we

is etched, the altered layer is dissolved away, and the

normal structure below it is revealed. recognise the presence of unstable individuals or groups resulting from the overstrain. When the elasticity of the

Without accepting all Mr. Beilby's conclusions, I think overstrained piece is tested by removing and reapplying is supported by the considerations I am now putting for

the idea of an altered and more or less amorphous laver the load, some of these tumble into new positions, making ward! inversible movements, which dissipate energy and produce

We have assumed that in normal crystallisation hysteresis in the relation of the strain to the stress although

the intermolecular forces lead to a normal piling, in which the strain is quasi-elastic. At the ordinary temperature these 1 Tourn. Iron and Steel Institute, 1000, unstable groups are gradually becoming resolved, no doubt Ewing and Humfrey. “The Fracture of Metals under Repeated

Alrernations of Stress," Phil Trans., vol. cc. A, 1002. 1. M 17, "On the Recovery of Iron from Overstrain," l'hil. Trans., 3 Beilby, “The Hard and Soft States in: Metals," Phil. Mag., August,

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each molecule touches six neighbours. But it may be con- creased power to resist the deteriorating effects of often jectured that some of them may take up pyramidal piling repeated stress. (touching twelve others) under the compulsion of strong I trust you will not feel I have abused the license of the forces---such forces, for example, as act on the superficial | Chair in presenting contributions to molecular theory that molecules of a surface that is being polished.

are for the most part in the nature of speculative sugger If this also occurs at a surface of slip, it gives us a clue tions, thrown out in the hope that they may some time to several known facts. It at least assists in explaining

lead to fuller and more definite knowledge. Remote the familiar result that metal is hardened by straining in they may seem to be from the concerns of the workaday the sense of being made less plastic. Again, it accounts engineer, they relate to the matter which it is his busifor the general increase of density which is found to take ness to handle, and to the rationale of properties, withou! place in such an operation as wire drawing. Further, if

which that matter would be useless to serve him. We a local increase of density occurs in the interior of a grain have attempted to penetrate into its very heart and subthrough piling of some molecules in the closer manner stance in order the better to comprehend the qualities and where repeated slips are going on, the concentration of functions on which the practical work of engineering relies. material at one place requires it to be taken from another ; The man whose daily business leads him through familiar in other words, the closer piling tends to produce a gap or tracks in a forest does well to stray rom time to time into crack in the neighbourhood where it occurs. This is con- the shady depths that lie on either hand. The eyes of his sistent with what we know of the development of cracks imagination will be opened. He will at least learn his through repeated alternations of strain.

own limitations, and, if he is fortunate, he may gain Recourse to the model shows that with pyramidal piling some clearing on a hilltop which commands a wider virs the polar axes point in so random a manner that the

than he has ever had before. aggregate may fairly be called amorphous. To illustrate this a group is shown with centres fixed at the corners of equilateral triangles.

SECTION 1. It is obvious that any pyramidal piling at a surface of slip tends to bar further slip at that particular surface. Hence not only the augmented hardness due to strain, but OPENING ADDRESS BY PROF. FRANCIS Goicu, M.A., D.Sc. the tendency in repeated alternations to lateral spreading F.R.S., WAYNFLETE PROFESSOR OF PHYSIOLOGY IN THE of the region on which slip occurs. The hardness due to

UNIVERSITY OF OXFORD, PRESIDENT OF THE SECTIOS. straining is, of course, removed when we raise the metal

" The investigators who are now working with such to such a temperature that complete recrystallisation occurs,

earnestness in a!l parts of the world for the advance of normal piling being then restored in the new grains.

physiology have before them a definite and well-understand Taking a previously unstrained piece, it is clear that the facility with which slip will occur at any particular

purpose, that purpose being to acquire an exact knowledge

of the chemical and physical processes of animal life and surface of slip in any particular grain depends not only of the self-acting machinery by which they are regulated on, the nature of the metal and on the orientation of the

for the general good of the organism. surface in question to the direction of the stress, but also In this admirable and concise manner the late Sir John on the amount of support the grain receives from its

Burdon-Sanderson described the aims and methods of neighbours in resisting slip there. In other words, for a given orientation of surface the resistance to slip may be

physiology. The words were spoken in 1881, when the

British Association last met in this historic city. It that said to consist of two parts; one is inherent in the surface time the subjects of Anatomy and Physiology formed :? itself, and the other is derived from the position of the subsection of the Section of Biology, and it was presided grain with reference to other grains. To make this point

over by this distinguished man, whose recent draih has or, think of a grain (under stress) deprived not only physiology but natural science of one of in which there is a gliding surface oriented in the most its most honoured leaders. His continuous work, exten'. favourable direction for slipping. Slip on this surface can

ing over a period of fifty years, was remarkable from take place only when its yielding compels the neighbours

many points of view, but in none more than the extent (which are also under stress) to yield with it, and the

of its scope.

Sanitary science, hygiene, practical medicine, surfaces in these on which slip is compelled to occur are,

botany, pathology, and physiology have all been illuminated on the whole, less favourably situated. Hence the original and extended by his researches. His claim for being ingrain cannot yield until the stress is considerably in excess

cluded among the great names in English science dors of that which would suffice to make it yield if it stood

not rest merely upon his acknowledged eminence as an alone, or had neighbours equally favourably inclined.

original and exact investigator, but also upon the influence Apply this consideration to the case of steel, where there

which, for four decades, he exerted upon other workers are two classes of grains : the ferrite, which is simply

in medical science, endowing their investigations with iron, and the pearlite, which is a harder structure. Slip

purpose and materially helping to give English physiology on any ferrite grain is resisted partly by the strength of

and pathology their proper scientific status, Many circum. the surface itself, and partly by the impossibility of its

stances contributed to make this influence widely felt : yielding without forcing slip to take place on neighbour

among these were the peculiar charm of his manner, his ing (harder) grains. Now suppose the structure is a very striking and commanding personality, the genuine enthugross one, such as Mr. Stead has shown may be found in

siasm with which he followed the work of others, the steel that is seriously overheated. On the large grains of devotion with which he advocated the use of experimental ferrite in overheated steel the resistance to slip will be

methods, his scientific achievements, and his extensive but little greater than it would be in iron, and, con

knowledge. All these qualities of mind and character • sequently, under an alternating stress fatigue of strength, marked him as one of those great masters who inspiru

leading to rupture, may be produced by a very moderate the work and mould the thought of a generation. It is amount of load. Mr. Stead' has shown how the effects

in tribute to his memory that, as one of his pupils anul of overheating can be removed by the simple expedient of

his successor in the Oxford Chair of Physiology, I utilice raising the steel to a temperature sufficient to cause re- this occasion for recalling such fruitful features of bis crystallisation-a homeopathic remedy that transforms the scientific conceptions as are expressed in the felicitous gross structure of the overheated metal into an ordinarily

phrase which I have quoted. fine structure, where no ferrite grain can yield without

Probably the most important of the many services which compelling the vielding of many pearlite grains. Hence Burdon-Sanderson rendered to English medical science was we find, as Rogers ? has demonstrated by experiment, that

that of helping to direct physiological and pathological steel cured by reheating from the grossness of structure

inquiry towards its proper goal. It will be admitted by previously produced by overheating, has an immensely in

all who knew him intimately that among his most I See especially a paper bv J. E. Sread and A. W. Richards on " The characteristic scientific qualifications were the insight with Restoration of Dangerously Crystalline Steel by Heat Treatment,” Journ. which he realised the essence of a physiological problem. of the Iron and Steel l»st., No. 2, 100%.

2 F. Rogers, " Heat Treatment and Fatigue of Steel," Journ. Iron, and 1 Address to the Subsection of Anatomy and Physiology, by J. Bardor Steel Inst., No. 1, 1905.

Sanderson, British Association Report, York, 1881.

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and the tenacity with which he kept this essential aspect who adopt · neo-vitalism are prepared to state not only in view. The faculty which enables the mind to review that certain physiological phenomena are, from the chemical the varied aspects of complea phenomena and to determine and physical point of view, inexplicable to-day, but that which oi these are mere incidents, or external trappings, from the nature of things they must for ever remain so. and which constitute the core of the subject, is one which This attitude implies that it is a hopeless business for the miers scientific worker must possess in a higher or lower physiologist to try by the use of more appropriate methods degree; it may, indeed, be confidently asserted that scien- to remove existing discrepancies between living and nontisic training, is successíul only in so far as it develops living phenomena, and this is accentuated by the use of a nice and just discrimination of this character. Many a peculiar nomenclature which, in attributing certain attain this capacity after several years of labour and phenomena to vital directive forces, leaves them cloaked elfort ; but in the case of rare and gifted individuals its with a barren and, from the investigator's point of view, possession comes so early as to seem almost an intuitive

a forbidding qualification. Endowment. In 1849, during his student days at Edin- It is of course possible in describing phenomena to burgh, Burdon-Sanderson showed by the character of his employ a new and special terminology, but since many earliest scientific work that he viewed the proper aim of aspects of the phenomena of living processes can be dephysiological inquiry as essentially the study of processes. scribed in accordance with physical and chemical concep

di the present time it may appear superfluous to dwell tions, the creation of a vitalistic nomenclature duplicates upon the importance of this standpoint, but fisty-seven terminology A double terminology is always Vears ago this aspect of the subject was rarely, in this embarrassing, but it becomes obstructive when it is of country, a stimulating influence in physiological work, such diversity that description in the one can

never in whilat, as regards pathology, the point of view taken by any circumstances bear any scientific relation to that in Burdon-Sanderson was, even in 1860, probably unique.

the other. In this connection it is somewhat significant The obvious fact that living processes occur in connec- that the one kind, namely vitalistic, is abandoned as soon tion with certain definite structural forms transferred as the observed phenomena to which it referred have been attention from the end to one of the means, and thus found to be capable of expression in terms of the other. ducation and research in physiology and pathology were The reason for this abandonment raises questions of prinalmost entirely confined to the elucidation of that struc- ciple, which appear to me to render it impossible for a tural framework in which the essential processes were now scientific physiologist seriously to employ vitalistic nomendisplayed and now concealed. Improved methods of micro- clature in describing physiological phenomena. Science is sopic technique revealed the complexity of this struc- not the mere catalogue of a number of observed phenoture, and minute anatomy absorbed the interest of the mena ; such a miscellaneous encyclopædia may constitute lew physiologists and pathologists who prosecuted re- what many people would describe as knowledge ; but searches in this country. Even when attention was directed science is inore than this. It is the intellectual arrangeto the living processes, it with

unconscious ment of recognised phenomena in a certain orderly array, anatomical bias, and detailed descriptions of structural and the recognition of any phenomenon is only the first framework were advanced as affording a sufficient scientific step towards the achievement of this end. The potent splanation of the character of the subtle processes which element in science is an intellectual one essentially conplayed within the structure. Yet upon the Continent the nected with mental grouping along one particular line, great physiologists of that time had long realised that that which tends to satisfy our craving for causative exphysiological study must ascertain the characters of these planation. Hence it involves the intellectual recognition processes, and that research conducted along experimental of widespread characteristics, so general in their distribulines could alone advance scientific physiology as distinct tion that they are termed fundamental. The most fundafrom scientific anatomy. In 1852 Burdon-Sanderson went mental of such characteristics are those which possess the from Edinburgh to Paris to study the methods used in widest intellectual sphere, and in natural science these physics and chemistry. Whilst there he came under the

are the broad conceptions of matter and motion which inspiring influence of one of these great Continental physio- form the essential basis of both chemistry and physics. logists, Claude Bernard, and his views as to the proper If this grouping is, in regard to any phenomenon, at preend of physiological inquiry received from this master sent impracticable, then this subject-matter cannot be ample confirmation. The sentence which I have quoted justly regarded as forming a part of natural science; from the York address sets forth with scientific precision though it might be considered as natural knowledge, and his enlarged conception of living phenomena, for whilst it in so far as this is the case in physiology, it appears to dscents that the characteristics of processes form the true me to be a confession of present scientific ignorance. If, aim of all physiological investigation, it defines the par- | however, it is boldly asserted that the nature of any ticular processes which should be investigated as chemical phenomenon is such that it can never by any possibility and physical, and it particularises two further aspects of be brought into accord with the broad conceptions which these, the machinery for their coordination described as I have indicated, then I fail to understand how it can srill-acting, that is automatic, and the raison d'être of claim to

bear an

relation to natural science, since, their occurrence, which is said to be the welfare of the ex hypothesi, it can never take its proper place in the whole organism. All these various aspects are strikingly causative chain which man forges as a limited but inexemplified in the progress of physiology in this country telligible explanation of the world in which he lives. and in the researches now being carried on both at home Only in so far as physiological phenomena are capable and abroad: their consideration may thus be not in

of this particular intellectual treatment and take part in appropriate in a general address such as it is my privilege this intellectual construction can we hope to obtain, how10 deliver to-day.

ever dimly, a knowledge of permanent backgrounds among At the outset it is desirable to refer to certain wide the shifting scenes of the living stage, and thus, by issues which are involved in the statement that the busi- | gradually introducing order amidst seeming confusion, ness of the physiologist is “ to acquire an exact knowledge claim that gift of prevision which has long been enjoyed of the chemical and physical processes of animal life.” by other branches of natural science. The limitation of physiology to ascertainable characters of Neo-vitalism, like its parent vitalism, is fostered by the a chemical and physical type does not commend itself to imperfect and prejudiced view which man is prone to take certain physiologists, physicists and chemists, who have in regard to his own material existence. This existence revived under the term * neo-vitalism the vitalistic con- is, for him, the most momentous of all problems, and it ceptions of older writers. They deny that physiological is therefore not surprising that he should assume that phenomena can ever be adequately described in terms of in physiology, pathology, and, to a lesser degree, in physics and chemistry, even if these terms are in the future biology, events are dealt with of a peculiarly mystic greatly enlarged in consequence of scientific progress. It character, since many of these events form the basis of is undoubted that there are many aspects of living pheno- his sensory experience and occur in a material which he mena which in the rxisting state of our knowledge defy regards with a special proprietary interest. He is relucexact expression in accordance with chemical and phvsical tant to believe that those phenomena which constitute the concrptions; but the issues raised have a deeper significance material part of his existence can be intellectually rethan the mere assertion of present ignorance, for those garded as processes of a physicochemical type, differing

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