vital actions; others are physical, others are chemical; but with regard to those of the first kind (vital), it is to be observed that there are two modes, each producing a special kind or class of symptom.

"(a.) Some symptoms are negative, i. e. they consist in the negation of vital properties. Of this kind are paralysis, anæsthesia, and the like; and it is at once evident that where only some links of the chain of vital processes, concurring to produce such complicated phenomena as voluntary movement and sensation, are exposed to observation, we cannot directly affirm wherein the negation lies. For example: the forefinger of the hand is paralysed: here is a negation of voluntary power over the muscles of that finger; and from the simple fact of the existence of the paralysis, we cannot say whether the muscles of the finger, the nerves of the forearm or arm, the spinal cord, or the brain, is affected. We may infer, from other circumstances, which is the more likely, but we can arrive at no definite conclusion from the fact itself.

"Symptoms of this negative character may be occasioned directly by some lesion easily recognisable by the anatomist, as, for example, the division of a nerve, softening of the spinal cord, or breaking up, by hæmorrhage or other causes, of the fibres in the cerebral motor tract; and thus many negative symptoms afford evidence of a solution of continuity in this or the other organ. They do not depend upon modifications of the nutritive or interstitial processes in those organs whose function it is to perform certain vital acts, but upon some interruption in the chain of organs by which these central vital acts are carried out.

"(b.) Other symptoms are positive, i. e. they consist in the excess or alteration of vital properties. Of this kind are spasms, pain, convulsions, and the like; and although we may not be able to say at once where the primary abnormal condition is, we can always assert that, inasmuch as the symptom is a modified vital act, it depends upon some modification of those nutritive processes which are the immediate or proximate cause of these and of all vital acts. For example: the forefinger of one hand is spasmodically contracted: here is an excess of muscular activity, and from the simple fact of its

existence we may not be able to say whether the muscles, the nerves, the spinal cord, or the brain, is primarily affected; but we are certain that, inasmuch as contractility and innervation are vital acts, and depend upon nutrition-changes in one or the other of the muscular or nervous organs, this spasm is due directly to some excess, or modification of those nutrition-changes.

"The difference, then, between negative and positive symptoms is this, that whereas the former may depend directly upon some such rough lesion as a solution of continuity, the pressure of a tumour, or other mechanical conditions, the latter (positive symptoms) must always depend directly upon minute, interstitial changes, which are the necessary conditions and proximate causes of vital acts. Distinct leisons of organs may be the remote causes of positive symptoms; a tumour may cause spasm; but such causes are remote always: the immediate cause is the change of nutrition, the modification of the interstitial process.

§ VII. "Convulsions are modifications of vital actions, and therefore depend upon modifications of physical conditions.

"It is no objection to this general proposition, that frequently, post mortem, we can discover no organic change in the brain or spinal cord, for convulsions belong to the second category of symptoms, and depend upon modifications of nutrition.

"We may find a tumour in the brain, or tubercular deposit in its meninges; we may find disease of the kidneys, or such general derangement of the organs as scrofula or rickets can produce; but wherever we may find these easily-discovered physical changes, they are not the immediate causes of convulsion, for convulsion is a modified vital act of muscularity and nervous force, and its proximate cause is in the nutritive condition of the nervous centres.

§ VIII. "Convulsions depend directly upon nutrition-changes

in the nervous centres.

"So long as spasm or paralysis, pain or anæsthesia, are confined to one muscle, or to a limited surface, it is possible, and often probable, that the lesion exists in the periphery, or in some channel of communication between the periphery and the centre; but when the disturbance involves all the muscles of a limb, of one side, and à fortiori, when all the muscles of the

body are involved, we conclude, and with reason, that the cause of disturbance is in that which is common to them all, viz., the nervous centre.

§ IX. "The immediate and proximate cause of convulsions is the same in all instances, when the convulsions are the same. "Convulsions differ from one another in different individuals, and in the same individuals at different times. In some the spasm is tonic, or partially tonic, in others clonic; in some, certain groups of muscles are specially affected, as the respiratory (hysteria); in others, different sets of muscles-those of the limbs, for instance (meningitis), or of the trunk-are involved (spinal disease).

"When there is merely a difference of locality, the proximate cause is the same in kind, and differs only in the situation or portion of the nervous centre it affects.

"When the difference is one of degree, a similar conclusion is warranted with regard to the degree of nutritive change; but when the convulsions differ in kind, we must infer that the proximate cause varies also in kind.

"But cases of convulsion, although presenting certain peculiarities in different individuals, are in the main alike; they have the same general features, pass through similar phases, and produce similar results. Their essential feature is involuntary muscular spasm, occurring in a paroxysmal form, varying in degree and local distribution, but affecting (in order to come within the definition of convulsions) at least one-half of the muscles of the body, and more commonly the whole.

"Now, whatever lesions we may find in the nervous centres, or in other organs, whether these are spiculæ of bone, hydatid cysts, thickened meninges, softened brain, calculus in the kidneys, or Bright's disease, such lesions are not the proximate causes of convulsions; for they are not present in all cases: they differ in locality and kind, and they bear no constant proportion to the symptom in question.

"The laws of nature are invariable, and so-called exceptions are either ignorances or errors; statistics of per-centage do but represent the fragmentary or fractional condition of our knowledge, and our necessity for their use is evidence that we have not yet given full expression to those laws, some portion only of

which we may dimly see and register. But our conviction is,and the possibility of science depends on such conviction,that the laws are fixed and invariable, and that similar effects must have similar causes.

"The immediate or proximate cause, therefore, of convulsions is the same in all instances; it is some change in the nutritive or interstitial processes of the nervous centres.

§ X. "The proximate cause of convulsions is an abnormal increase in the nutritive changes of the nervous centres.

"The vital processes, muscular innervation and contraction, are correlated to the physical processes of assimilation and disintegration, and the excess of the one depends upon the augmentation of the other.

"As the chemical composition and decomposition proceeding in the cells of a galvanic battery give rise to or occasion the so-called 'current' in the wire which unites its poles, so the nutritive processes of assimilation and disintegration in the centre of motility, give rise to or occasion the impulse which shall pass through the nerves, and induce contraction of the muscles. If the chemical changes are increased in quantity or force, there is a correlative increase in the quantity or tension of the galvanic stream. If the nutritive processes are accelerated or increased, there is a corresponding augmentation of the vital result. In the former case the wire may become heated; in the latter, instead of simple tonicity, there may be spasm.

"The nutrition-changes which in health produce, as their vital effect, stability of tissue, secretion, sensation, and motion; occasion hypertrophy, flux, pain, and spasm, when augmented in degree.

"There are two modes in which the nutrition-changes may be so modified as to occasion abnormal vital acts, or positive symptoms. These are (first) acceleration, or increase in relation to time, and (secondly) an increase of mobility. Of the first the period of infancy is an example; of the second, scrofulosis or tuberculosis may be used as illustrations. In youth there is great rapidity of nutritive change, and there is also great vital activity with its tendencies to abnormal increase; in tuberculosis there is also rapidity, but there is besides this an instability of structure and a morbid readiness for change.

§ XI. "The remote causes of convulsion are such as induce an abnormal increase in the nutrition-changes of the nervous centres.

"The proximate cause being the same in all instances, the remote causes vary; but they agree in this, that they affect the nutrition of the nervous centres. Identical remote causes must produce identical effects (i. e. if all the causative conditions are identical); but in their examination we enter upon a deeply complicated assemblage of conditions, and cannot at all times trace the relation between them.

"What we have now to do is to indicate the general mode or modes in which these remote causes are carried forward to, and are productive of, the proximate conditions upon which convulsions depend."

The diseases commonly spoken of as the causes of convulsions-viz., tumour of the brain, meningitis, and the like-must be regarded as their remote causes, and the diagnosis of a convulsive disease is the discovery of the latter. In all cases, the particular organic condition upon which convulsions immediately depend-i. e. the proximate cause of convulsions-is the same. We have, therefore, to point out now the different modes in which it may be brought about.

A. It may be idiopathic, or primary; a morbus per se. In such cases, the sole deviation from healthy structure is the intimate nutrition-change: the only variation from normal function is the convulsion.

That such convulsive disease does exist thus primarily is the only warrantable induction from experience, and a perfectly logical deduction from general pathologic laws. For, on the one hand, minute investigation has hitherto failed to discover any further lesion; and, on the other, while nutrition is known to suffer changes from the healthy standard, there has not been shown any reason for excluding from the possibility of such changes the nervous centres.

To controvert this position, à posteriori, it must be shown that in all cases there is some further deviation from healthy structure to oppose it successfully, upon à priori grounds, it must be proved that, while in the osseous or membranous tissues it is quite possible for such a nutrition-change to occur as shall result in a spicula of bone, in the nervous tissue it is quite impossible