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questions and problems, and is likely to continue to be a popular manual on the outlines of inorganic chemistry and chemical philosophy.

MESSRS. MACMILLAN AND CO., LTD., have issued a new and revised edition of stage 'vi. of Mr. Vincent T. Murché's "Object Lessons in Elementary Science," the price of which is 2s.

A FIFTH edition of Mr. W. W. Fisher's "Class Book of Elementary Chemistry has been issued by the Clarendon Press, Oxford. The text has been entirely revised, and numerous additions have been made. Several chapters on organic chemistry, intended to serve as introduction to this division of the subject, have been included in the new edition, which is now in line with the present state of knowledge of the subjects dealt with in the volume.

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Calculating from these elements the positions at the times of Prof. Perrine's observations, it was found that the residuals were satisfactorily small, but for five intermediate dates, on which observations were secured, they proved to be larger than were expected. Dr. Ross accepts this result as evidence of the large periodic perturbations, chiefly solar, to which the satellite is subjected. The above elements indicate that this satellite revolves about Jupiter in a direct orbit, for although a retrograde orbit was computed and found to fit the three primary observations, it did not agree with the positions obtained from the intermediate observations.

An ephemeris, covering the period July I to November 13, from which the following positions are taken, accompanies Dr. Ross's paper :p. S.

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53 58 290 59

On October 4 the distance will still be 59', but after that date it will slowly decrease, until on November 13 it will be only 18'.

According to a note communicated by Prof. Perrine to the Astronomical Society of the Pacific, and reproduced in No. 4035 of the Astronomische Nachrichten, Dr. Ross has also computed the orbit of Jupiter's sixth satellite. This satellite, like the seventh, moves in a direct orbit, its period being 242 days. The eccentricity of the orbit is large, amounting to 0-16, and the inclination to the plane of Jupiter's equator is about 30°. The mean distance of the satellite from Jupiter is about seven million miles. Thus the periods, and therefore the distances from Jupiter, of the sixth and seventh satellites are nearly alike, their orbits mutually interlocking. Otherwise the two orbits are dissimilar.

THE FORMATION OF THE NEW NORTH POLAR CAP ON MARS. According to Mr. Lowell's observations, as re. corded in No. 22 of the Lowell Observatory Bulletins. the first frost of this year in the Arctic regions of Mars occurred on May 19. The region wherein the phenomena were observed had been under daily scrutiny since coming into view on May 11, but no new feature had been discovered. However, on May 19 an enormous, unmistakably white patch was which extended from the western edge of the old cap to a point on the terminator about one and a half times the old cap's diameter away, and reached down to latitude +63°. The deposit was so thin on its northern edge that the band girdling the old cap could be plainly seen showing through it, but on May 20 a bright nucleus formed on the southern edge of the frost-bound area.

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The date of the first observation corresponds to August 20 in our calendar, and is 126 days after the summer solstice in the northern hemisphere of Mars. In 1903 the first frost effects were observed on Mars about 128 days after the summer solstice; thus the recent observation strongly confirms those made in 1903.

LIQUID AIR-PRODUCTION AND APPLICATIONS.'

more correct.

IN the former of these papers the author details experiments showing the trustworthiness of a German silver platinum couple to measure temperatures in the neighbourhood of those of liquid air and liquid and solid hydrogen. The electric resistance of metals is an unsafe guide at very low temperatures, and the manipulation of gas thermometers involves much time and care. A thermoelectric junction would be much more convenient if trustworthy. That it is trustworthy the experiments go to show, but only within limits. If the constants of the formula for interpreting the observations be determined at temperatures between 90° and 123° abs., the formula will then give the temperature of solid hydrogen at low pressure as 15° 27 abs., whereas if the constants be deduced from experiments at a lower temperature, 20° to 771°, the interpretation formula then makes the temperature of solid hydrogen at low pressure 13° lower, 1.e. 135 abs., which the author considers Bearing in mind that at this very low temperature a difference of 11° is equivalent to a difference of 37° at the ordinary temperature, we see that the method has no confirmatory value, and can itself be trusted only over the range for which it has been verified by the careful use of gas thermometers. If, therefore, helium be procured in sufficient quantity for liquefaction or solidification, its lower temperatures, possibly within 5° of the absolute zero, will have to be ascertained by the low-pressure helium thermometer. For ranges of temperature over which its indications can be verified, the thermoelectric junction thermometer will have a useful sphere of work in saving the inconvenience of employing gas thermometers. Among important cautions given by the author is a warning that junctions made with soft solder are affected by the low temperature. The junctions should be made with hard silver solder, and the indications at the temperature 1 "On the Thermo-electric Junction as a Means of Determining the Lowest Temperatures, and n Liquid Hydrogen and Air Calorimeters." Papers by Sir James Dewar, read before the Royal Society, June 8, 1905.

of liquid oxygen compared before and after exposure to the temperature of liquid hydrogen, to see whether there has been any change produced. A German silver platinum junction was employed, but as the result of his experience the author recommends German silver gold.

The paper on " Liquid Hydrogen and Air Calorimeters" gives an account of experiments in which the specific heats of substances are determined by measuring the quantity of liquid air or hydrogen which they vaporise in falling through a given range of temperatures. From these experiments it appears that, at temperatures between those of these two liquids, ice has only one-third of its specific heat at ordinary temperature, graphite has only one-tenth, while diamond has as little as one-nineteenth of its ordinary specific heat. The second part of this paper deals with the latent heats of the volatile liquids, that of hydrogen being given as 121 or 122 calories, of oxygen 3115 calories, and of nitrogen 50-4 calories. The latent heat of liquid air is not yet definitely determined, but when there is a high percentage of oxygen it is about 54 calories. The specific heat of hydrogen is found to be substantially the same, whether the substance be liquid, occluded, or gaseous.

The employment, just mentioned, of liquid air to determine the specific heat of substances may be called a practical application, though, so far, its utility is limited to scientific research; and the present time, ten years after the introduction of the new and comparatively economical method of producing it, is suitable for a review of its applications generally, the further developments in the methods of producing it, and the extent to which it has been possible so far to realise the expectations founded on the appearance of the new method of production.

It will be remembered that down to the year 1895 the method of liquefying air developed and employed by Olszewski and Dewar was what is called the cascade method, in which a gas condensed at high pressure is vaporised at a much lower pressure, so as to produce a much lower temperature, one low enough, perhaps, to condense a more volatile gas highly compressed. Thus nitrous oxide was made to produce liquid ethylene at a temperature below -90° C., and the ethylene, boiled at low pressure, similarly produced liquid oxygen, nitrogen, or air at 140° C. These liquids, boiling in the open, reduced their residual portions to their well known boiling points, and, boiled at low pressure, produced much lower temperatures, but in no case low enough to act in the same way as a means of liquefying compressed hydrogen, which is so volatile that its critical temperature is below the lowest obtainable by boiling the atmospheric gases at low pressure. The nearest approach to the liquefaction of hydrogen was Olszewski's imitation of Cailletet's combination of the cascade system with sudden expansion. He obtained a similar result-the brief appearance of an evanescent mist, which just sufficed to show that hydrogen was, under proper conditions, liquefiable. An ingenious means for getting below the lowest temperatures obtainable on the cascade system by boiling oxygen or nitrogen at low pressure was adopted by Olszewski and Dewar, who mixed hydrogen, the former with oxygen, the latter with nitrogen, in the hope of making a substitute for a natural gas of intermediate properties, which, boiling at low pressure, would give a temperature low enough for the liquefaction of compressed hydrogen on the cascade system. Both attempts were unsuccessful, though Dewar thought that the nitrogen jelly behaved as if it had some condensed hydrogen in solution.

At this stage there appeared a new and more powerful method for cooling and liquefying gases, the selfintensive system, by which compressed gas, allowed to cool itself by expanding to low pressure at a free orifice, has its cooling accumulated by an interchanger, and so intensified continually. Thus oxygen, nitrogen, and air starting from ordinary temperatures, and hydrogen starting from a temperature below -200° C., can be made to cool themselves to the liquefaction point, and gradually liquefy themselves at ordinary pressure without the help of any less volatile liquid to assist the fall of temperature. With such apparatus available, great expectations were indulged in as to the future possibilities of liquid air. As with electricity, the enthusiast and the impostor were

soon at work, making unlimited promises to attract the interest of the public, and company schemes to attract their money. Liquid air as a source of power was going to eclipse and replace steam and electricity. As an artificial refrigerant it was to banish ice, ammonia, sulphur dioxide, and carbonic acid. In surgery it was soon to be the only anæsthetic, antiseptic, and caustic employed; in medicine it was to cure consumption and many other diseases. Our prominent scientific men cannot claim much credit for doing their duty to the public in this matter. In a few reported interviews some of them mildly recommended caution. In this country only one prominent worker with liquid air plainly warned the public at the beginning of this boom that such promises were either foolish or fraudulent, and declared that on the score of expense liquid air, as made by the new method, could never compete with steam as a source of power or with ice as a source of refrigeration. The last ten years have too fully justified the warning; but in the meantime large sums of money were extracted from the public in America by fraudulent liquid air companies, one of which attempted to continue operations in this country; and many business men in England held over orders for new refrigerating plants for some years, for fear lest, as soon as they had put one down, they might find it superseded by a liquidair contrivance. Apart from scientific research, the nearest approach to a commercial application of liquid air began last autumn, when experiments were given at music-halls under the name of the " Magic Kettle." The performance was anything but a popularising of scientific knowledge, of which the performers themselves in most cases had none; besides which they purposely deepened the mystery of the matter by adding a little juggling, and making misleading statements.

Air liquefiers of the best make are now such perfect machines that they seem to offer no scope for improvement within the existing system. The chief attempt to improve the system consists in substituting an engine to do work for the free-expansion valve, in order to obtain more cooling for a given amount of compression. This device, in the form of a turbine, was discussed as early as 1895, but rejected on the ground of complication. In 1896 Lord Rayleigh suggested it in a letter to NATURE, and others have proposed or attempted it since. Thermodynamically it would be a great gain; but in apparatus of this kind a thermodynamic gain often actually involves a greater practical loss, owing to the importance of simplicity. In Comptes rendus, vol. cxxxiv. pp. 1568-1571, is an account of such an apparatus made by M. G. Claude, which is declared to have been entirely successful. As this is purely a question of economy and convenience, which are dominating factors commercially, the fact that this apparatus is not yet displacing others makes it likely that the complications involved are found to be a serious stumblingblock. They have hitherto prevented the adoption of a similar device in commercial refrigerating machines working with ammonia and carbonic acid, which are now made on such a very large scale that in them, if anywhere, the thermodynamic gain would outweigh the complications.

One of the most promising practical applications proposed for liquid air has been the manufacture of oxygen from air by liquefying it and letting the nitrogen boil away before the oxygen, separating them by distillation. Theoretically the power, that is, the cost, required should be small. The latent heat taken up by the two gases separately in volatilising should balance that given out by the air in condensing. One of the prominent names associated with attempts of this kind is that of Pictet, who was long believed to have liquefied oxygen and hydrogen at the time when Cailletet undoubtedly produced a mist of oxygen. In New York Pictet was associated with others in an attempt of this kind under a patent (U.S.A.) in which he commits the fallacy of expecting the gases to separate at a low temperature, but while both are still in the gaseous condition, the greater density of the oxygen taking it to the bottom of the container! The oxygen did not drop, but the scheme, the patent, the fallacy, and the investors' money did. Pictet next appeared with a French patent, in which the U.S. patent fallacy was replaced by another. He arranged to make

a gain of cooling by letting liquid air vaporise at a lower temperature than that at which it had condensed, taking up more latent heat at the lower temperature than it had given out at the higher; and he overlooked the fact that the difference would be balanced by the specific heat given out by the liquid while being cooled to the lower temperature! Under a fresh patent in England Pictet has now for some years been associated with powerful supporters in installing a large and costly plant at Manchester with the same object. None of the former fallacies appear in the new patent. Whether practical success will attend the effort remains to be seen.

The liquid oxygen, or air rich in oxygen, obtained by distillation from liquid air, if mixed with a good combustible, such as cotton wool, makes an explosive. The Austrian military authorities, and the engineers engaged in tunnelling under the Alps, both made long and careful trials of such explosives; but the inevitable arrangements were too cumbrous, and the results too uncertain.

The nearest attempt to make what is called a practical use of liquid air is that of Dr. Allan Macfadyen (see NATURE, June 18, 1903, p. 152, and October 22, 1903, p. 608). By freezing the bacilli of typhoid in liquid air he makes them brittle enough for trituration in a mortar. By centrifugalisation the intracellular poison can then be separated from more fibrous material, and then by the methods of Pasteur an anti-typhoid serum prepared which promises to be of real value.

The most pronounced successes of liquid air have been in connection with scientific research. It was with liquid air made by the self-intensive process with a Hampson machine that Sir William Ramsay discovered krypton, xenon, and neon, that Prof. Rutherford and Mr. Soddy proved the emanations of radium and thorium to be condensable and vaporisable, that Ramsay proved the evolution of helium from radium emanations, and many other important investigations were carried out. Finally, it was by an extension of the same process that hydrogen was liquefied.

THE MEETING OF THE BRITISH
MEDICAL ASSOCIATION.

A
NUMBER of valuable and instructive papers were
contributed at the recent meeting of the British
Medical Association at Leicester, but the majority were
technical and of a medical nature. The following, in
addition to those described last week (p. 330), are, how-
ever, of more general interest :-

In the section of medicine, Dr. Nathan Raw (Liverpool) read a paper on human and bovine tuberculosis, with special reference to bovine infection in children. He said that while agreeing with the German view that there were decided differences between the bovine and human tubercle bacilli, he believed that bovine tuberculosis was a danger to human beings.

Bovine tuberculosis affected young people, was traceable to infected milk, and infected the tonsils, the alimentary tract, the glands, and, through the blood, the meninges, the bones, the joints, and other parts, while human tuberculosis was air-borne, and infected adults by way of the lungs as pulmonary phthisis. In evidence of this Dr. Raw indicated the rarity of pulmonary phthisis in infants and children, and, on the other hand, the comparative rarity of other than pulmonary lesions in adults, and suggested, further, that early tuberculous disease, presumably bovine, appeared to be protective against phthisis, as the development of pulmonary tubercle was relatively rare in those of a strumous diathesis who had suffered in infancy from bone and gland lesions.

In conclusion, Dr. Raw alluded to the frequency of tuberculosis among cattle, and the importance of the inspection of cattle and dairies.

Dr. F. J. Poynton (London) gave the results of his experience of milk to which sodium citrate had been added in the feeding of infants. The addition of sodium citrate to milk results in the formation of calcium citrate, and milk so treated forms a much finer curd and is more digestible than untreated milk. The sodium citrate may

be added to the amount of 1 to 2 grains to the fluid ounce of milk.

In the section of ophthalmology, Prof. Hess (Würzburg) demonstrated by a series of beautiful drawings the influence of light in causing a migration of pigment in the retina of cephalopods. He had found in these eyes visual purple which had hitherto not been detected in any invertebrate. All cephalopods studied by him showed this pigmentary migration within the retina, but the rapidity of the migration differed in various species, and it was different in different parts of the same retina, especially in the small horizontal stripe which contained very long and small rods, and corresponded evidently to an area of maximum vision. In the section of tropical medicine, Mr. R. Newstead, of the Liverpool School of Tropical Medicine, read a paper on ticks concerned in the dissemination of disease in man, and gave a description of the Ornithodorus moubata which conveys tick fever, a spirillar infection, in the Congo Free State.

The

Mr. Newstead had found that in many respects the habits of the Ornithodorus moubata were not unlike those of Argas persicus, but the inert character of the larva of Ornithodorus moubata was unique among the Ixodine, in that it passes the whole of its life within the egg. female Ornithodorus moubata laid eggs which hatched, not as larvæ, but as nymphæ, although on the ninth day the larva was fully formed and the egg shell split, but the young tick remained until the fifteenth day, when as a nymph it escaped simultaneously from its larva covering and egg shell.

were

Dr. Graham (Sierra Leone) contributed a paper on guinea worm and its hosts. He had found that the incidence of the disease corresponded with the incidence of a cyclops, the presumed intermediate host, both seasonally and as regards its maximum manifestation.

A

SOME ASPECTS OF MODERN WEATHER FORECASTING.1

FTER referring to the circumstances in which he was called upon to deliver the evening discourse in the absence of the Dean of Westminster, the lecturer explained that he had chosen the subject, not because he regarded weather forecasting as the only, or, from the scientific point of view, the most important practical branch of meteorology, but because, in a general sense, the possibility of its application to forecasting-the deduction of effects from given causes-was the touchstone of scientific knowledge.

The process of modern forecasting was illustrated by the daily weather charts of the period from February 1, 1904, up to the evening of February 12, which exhibited the passage over the British Isles of a remarkable sequence of cyclonic depressions, reaching a climax in a very deep and stormy one on the evening of the lecture. It was thus pointed out that the barometric distribution and its changes were the key to the situation as regards the weather, and this was supported by exhibiting the sequence of weather accompanying recognised types of barometric changes, as shown in the self-recording instruments at the observatories in connection with the Meteorological Office.

Some cases of difficulty in the quantitative association of rainfall or temperature changes with barometric variations were then illustrated. The barometric distributions in the weather maps for April 8 and April 16, 1903, were shown to be almost identical, and yet the weather on the later date was 10° colder than on the earlier. The observatory records for June 22, 1900, showed that a barometric disturbance of about the fiftieth of an inch, too small to be noticed on the scale of the daily charts, passed across the country from Valencia to Kew, over Falmouth, in about twenty-four hours, and produced at each observatory characteristic changes of temperature and wind, and also in each case about a fifth of an inch of rainfall.

Some examples of the irregularity of motion of the centres of depressions were also given, including one which travelled up the western coasts of the British Isles on October 14 and 15, and down the eastern coasts on

1 Abstract of a discourse delivered at the Royal Institution of Great Britain by Dr W. N. Shaw, F.R.S.

October 16 and 17, 1903, one which developed from scarcely visible indications into a gale on December 30, 1900, and one which disappeared, or filled up,' as it is technically called, on February 6, 1904. The conclusion was drawn that the suggested extension of the area of observation by means of wireless telegraphy from ships crossing the Atlantic would not immediately place forecasting in the position of an exact science, but would add greatly to the facilities for studying the life-history of depressions.

The irregularities and uncertainties illustrated by the examples given might be attributed in part to the complexities of pressure due to the irregular distribution of land and sea in the northern hemisphere. Charts of the mean isobars for the world for January and July showed greater simplicity of arrangement in the southern hemisphere, where the ocean was almost uninterrupted, than in the northern hemisphere, where there were alternately large areas of sea and land. The comparative simplicity of the south as compared with the north was also illustrated by a chart representing an attempt at a synoptic barometric chart for the world for September 21, 1901.

The simplification of the barometric distribution at successively higher layers of the atmosphere, as illustrated by Teisserenc de Bort's chart of mean isobars at the 4000-metre level, was pointed out, and illustrations were also given of the method of computing the barometric distribution at high levels from observations at the surface, using data obtained from observations at high-level observatories, or those made with balloons and kites.

Some indication of the connection between the complexity of the surface and the simplicity of the upper strata might be established by means of careful observations of the actual course of air upon the surface and the accompanying weather conditions.

Α

The actual course of air along the surface was often misunderstood. The conventional S-shaped curves representing the stream lines from anticyclonic to cyclonic regions were shown to be quite incorrect as a representation of the actual paths of air along the surface. diagram contributed to the Quarterly Journal of the Royal Meteorological Society showed the computed paths for special case of a storm of circular isobars and uniform winds, travelling without change of type at a speed equal to that of its winds. An instrument made by the Cambridge Scientific Instrument Company to draw the actual paths of air for a number of different assumptions as to relative speed of wind and centre, and of incurvature of wind from isobars, was also shown, and the general character of the differences of path exhibited under different conditions was discussed.

In illustration of the application of these considerations to practical meteorology, it was noted that rainfall is an indication of the existence of rising air, and conversely the disappearance of cloud may be an indication of descending air. It was further noted that if the ascent and descent of air extended from or to the surface, the actual paths of air along the surface, as traced from the direction and speed of the winds, ought to show convergence in the case of rising air and divergence in the case of descending air.

The chart for April 16, 1903, was referred to for an obvious case of dilatation or divergence of air from a centre corresponding with fine weather, the centre of the area of divergence being specially marked "no rain," and the actual trajectories or paths of air for two different travelling storms were contrasted, to show how the rainfall might be related to the convergence of the paths of air. The two occasions selected were (1) the rapid travelling storm of March 24-25, 1902, and (2) the slow travelling storm of November 11-13, 1901. The trajectories or actual paths of air for these two storms had been constructed from two-hourly maps drawn for the purpose from a collection of records of self-recording barographs, &c. Those for March 24-25 showed the paths to be looped curves with very little convergence, whereas those for the

1 The Meteroological Aspects of the Storm of February 26-27, 1903. Q.J R. Met. Soc., vol. xxix. p. 233, 1903.

2 See Pilot Charts for the North Atlantic and Mediterranean, issued by the Meteorological Office. February, 1904.

storm of November 11-13 showed very great convergence; so much so that if four puffs of smoke could be imagined starting at the same time from Aberdeen, Blacksod Point, Brest, and Yarmouth respectively, and travelling for twenty-four hours, they would find themselves at the end of the time enclosing a very small area in the neighbourhood of London.

Corresponding to this difference of convergence as shown by the paths was the difference of rainfall as illustrated by two maps showing the distribution of the rain deposited from the two storms. The first, with little convergence, gave hardly anywhere more than half an inch; the second, with its great convergence, gave four inches of rain in some parts of its area.

BREATHING, IN LIVING BEINGS.

64

IT has been said that the most striking facts connected with respiration are its universality and its continuity. In popular language the breath is the life." Breathing is not only a sign of life, it is a condition of its existence. Permanent cessation of breathing is regarded as a sign of death. Link up with this the icy coldness of death and you have two significant facts.

Respiration and calorification are therefore intimately related; in fact, calorification is one form of expression of the results of respiratory activity.

The popular view of respiration is an inference from what is observed in man and animals. During life the rise and fall of the chest goes on rhythmically from the beginning to the end. The respiratory exchanges effected in the breathing organs-lungs or gills-constitute "external respiration.' This, however, scarcely touches the main problem, viz. what is called "internal respiration,' or tissue respiration-i.e. the actual breathing by the living cells and tissues which make up a complex organism.

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We are told that man does not live by bread alone. We know he requires, in addition, solids, fluids and air. Taking these to represent the three graces, then air is of all the graces best.

The higher animals have practically no reserve stores of air-unlike what happens with the storage of fats and proteids-and hence the necessity for mechanisms by which air is continually supplied to the living tissues, and also by which the waste product of combustion, viz. carbon dioxide, is got rid of. Closure of the wind-pipe, even for a few minutes, brings death with it from suffocation. The entrance of oxygen is prevented and the escape of carbon dioxide is arrested.

The process of breathing is common to all living beings -to plants and animals alike. It consists essentially in the consumption of oxygen by the tissues and the giving out of carbon dioxide. It is immaterial whether the animals or plants live in water or air, the principle is the same in both cases. Living active protoplasm demands a supply of oxygen.

All the world's a stage. The human body is at once a stage, and a tabernacle-a vast theatre-and the myriads of diverse cells of which it is composed, the players.

66

The cells or players, as active living entities, not only require food, but they require energy. The respiratory exchanges in and by the living cells provide the energy for the organism. This breathing by the cells is called internal respiration." In a complex organism, therefore, the respiratory exchanges represent the algebraic sum of the respiratory activity of the several tissues that make up the organism. The various tissues, however, breathe at very unequal rates.

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In one of his charming contes philosophiques," Voltaire describes the visit of a giant of Sirius to our planet. Before reaching his journey's end he would have to traverse an aërial medium, and on arriving would see before him a fluid medium in continual movement, and tracts of solid land. After investigation-or no doubt he would be told, even though he was not personally conducted that the water surface of this our globe is two

1 Abstract of a discourse delivered at the Royal Institution of Great Britain by Dr. William Stirling.

and a half times greater than the land surface. He would discover that there are animals that live in air, others in water, and again others on land. Our visitor would find out that the respirable media are two-water and airand that there are 210 parts of free oxygen in a litre of air, while there are only 3-10 dissolved in a litre of

water.

Had Voltaire's friend paid us another visit during the present century, we should be able to tell him that the water of the Thames above London contains 7.40 c.c. of O per litre; at Woolwich only 0.25, the decrease being due to the pollution of the river. Putting it broadly, water contains only 3-10 parts per litre, while air contains 210. Water-breathers under good conditions have twenty times less O than air-breathers. It is as if air-breathers on land had the percentage of O, reduced to 1.

He would also be told that carbon dioxide-CO,-is also remarkably soluble in water, and readily combines with certain bases present in water; thus water forms an admirable medium into which an animal may discharge its effete and poisonous irrespirable CO,.

He would also be told that our blood contains 60 volumes per cent. of gases, and that there is more O and less CO2 in arterial blood than in venous blood.

Perhaps the name of Sir H. Davy might be whispered to him, for he was one of the first to detect the presence of gases O and CO, in blood.

In story, one has heard of the "Quest of the Holy Grail. I have even listened with rapt attention to an entrancing lecture on the "Quest of the Ideal." For the cell, the quest is the quest of oxygen,' and it is not happy until it gets it.

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We speak of a distinction between air-breathers and water-breathers. If, however, we push the matter to its ultimate issue, we find that all our tissues-and equally those of plants-live in a watery medium; in us the fluid lymph which exudes from our capillary blood-vessels, and in plants in the sap. Thus we come upon what at first seems a paradox, but is not so; all our cells not only live in water, but they live in running water. They are bathed everywhere by the lymph which is the real nutrient fluid for our cells. Thus, in its final form, all respiration is actually aquatic. The process of internal respiration, besides other conditions, requires the presence of a certain amount of water. In fact, all vital phenomena require the presence of water.

The unity and identity of the process in animal and vegetable cells, as the theatre of combustion, is the striking fact. The means by which the necessary oxygen is brought to the cells is as varied as the forms of animated organisms themselves. This function exists for the cells, and not the cells for the function.

If the mountain will not go to Mohammed, Mohammed must go to the mountain. There are, at least, two principles on which animal cells obtain oxygen.

The air or water containing air is carried to the cells. This is the principle adopted in the lower invertebrates, as in sponges and with regard to certain air-breathers such as insects.

The other principle is this, that an intermediary carries the respiratory oxygen from some more or less central localised or diffuse surface to the cells. This intermediary is the blood-an internal medium of exchange. The fluid part of the blood may carry the oxygen supply and remove the carbonic dioxide waste. This is the case in many of the invertebrates, and it reaches its highest development in the vertebrates. Hence in them the circulating and respiratory systems reach their fullest development.

In most invertebrates the fluid part of the blood contains the nutritive substances and also the oxygen and carbonic acid. In the vertebrates, the hæmoglobin of the red blood corpuscles carries the oxygen from the gills or lungs to the tissues, whilst the CO, is contained in and carried chiefly by the blood plasma from the tissues to the gills or lungs. It is singular that in the cephalopods, such as the squid and cuttle-fish, the blood is bluish in tint; and this is due to the presence in the plasma of a respiratory pigment called hæmocyanin. This body has a composition like that of hæmoglobin, but copper is substituted for the iron of the hæmoglobin. Copper also exists in organic

combination in the red part of the feathers of the plantain

eater or turaco.

The real aristocracy with genuine blue blood are the crab, lobsters, squids, and cuttle-fishes.

Perhaps one of the most striking ways of dissociating this accessory mechanism from the activity of the cell itself is by the use of a poison. When a person is poisoned by coal gas, what happens? The coal gas contains carbon monoxide. This gas does not poison invertebrate animals or plants. Still it kills vertebrate animals. Why? It does not kill by acting on the living cells, only by depriving them of oxygen and asphyxiating them. It combines with the respiratory pigment hæmoglobin. Chloroform, ether, and similar drugs destroy the actual life of the cell elements by destroying their irritability.

In 1771, Priestley found that air vitiated by combustion of a candle, or by the breathing of animals-such as mice -could be made pure or respirable again by the action of green plants.

Under certain conditions, however, Priestley found that plants gave off carbonic acid, and the air did not support combustion or animal life. He regarded these as "bad experiments," and he selected what he was pleased to regard as good experiments," i.e. those in which the air, rendered impure by the respiration of animals, was rendered respirable by the action of green plants.

44

In 1779 John Ingen-Housz published his " Experiments on Vegetables, discovering their great power of purifying the common air in sunshine, and of injuring it in the shade and at night."

He confirmed Priestley's observations that green plants thrive in putrid air, and that vegetables could convert air fouled by burning of a candle, and restore it again to its former purity and fitness for supporting flame, and for the respiration of animals-or, as he puts it, plants correct

bad air."

In 1787 Ingen-Housz, an English physician at the Austrian court, found that only in daylight did green plants give off oxygen. In darkness, or where there was little light, they behaved like animals so far as exchange of gases is concerned, i.e. they used up oxygen and exhaled carbonic acid. He found also that all roots, when left out of the ground, yielded by day and by night foul air, i.c. carbonic acid.

In the same year, 1804-the year of Priestley's deathNicolas Theodore de Saussure, a Swiss naturalist and chemist, published his "Recherches Chimiques sur la Végétation" (Paris, 1804), a veritable encyclopædia of experiments of the effects of air on flowers, fruits, plants, and vegetation generally, and on the effects of these on atmospheric acid.

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It is an old adage the exception proves the rule. The exception "probes" the rule as the surgeon's probe probes wound. The tactus eruditus of the surgeon, by his probe-indeed an elongated tactile sense-enables him to discover the presence or absence of a body in a wound. Had Priestley used the probe of a bad experiment, he in all probability would have anticipated the discovery of Ingen-Housz.

Some of you, no doubt, recollect the words of Goldsmith's famous description of his own bedroom and of the furniture of the inn

"The house where nut-brown draughts inspired." And how his imagination stooped to trace the story of"The chest that contrived a double debt to say, A bed by night, a chest of drawers by day.'

As to himself he tells us how

"A night-cap decked his brows instead of bay, A cap by night-a stocking all the day." Green plants contrive a double debt to pay; they give off oxygen by day, and at night exhale CO,.

How do the vast number of plants, the microbes, the bacteria without chlorophyll get oxygen? Most of them get it as we get it. Some, however, cannot live in pure oxygen and are anaerobic, such as the micro-organisms that cause tetanus, malignant cedema, and those that set up butyric acid fermentation.

Pushing the matter still further, it is extremely probable that the oxidation processes in our tissues are largely due to the presence of oxydases.

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