By none were these phenomena more care fully studied than by Whytt and Prochaska. In i764 Whytt published his " Observations on Nervous Diseases," a work full of the most valuable clinical and practical information. ln the first chapter of this book, " on the structure, use, and sy mpathy of the nerves," he enumerates various instances of sympathetic actions, and discusses the mode of their production. To show that he rewarded in this light the actions which we are now considering, I shall quote one which he adduces as an example. Ile says : " When the hinder toes of a frog are wounded, immediately after cutting, oft' its head, there is either no motion at all excited in the muscles of the legs, or a very inconsider able one. But if the toes of this animal be pinched, or wounded with a penknife, ten or fifteen minutes after decollation, the muscles not only of the legs and thighs but also of the trunk of the body are, for the most part, strongly convulsed, and the frog sometimes moves from one place to another." Whytt's most important work, in which this subject has been most fully discussed, is the essay on the vital and other involuntary motions of animals, published ten years earlier, in 1754. This physiologist was deeply imbued with a righteous dread of materialism, which led him to such extraordinary lengths in spiritualism, that he ascribed every action and movement of the body to " the immediate energy of the mind or sentient principle;" while he completely repudiated all notion of any mechanical dispo sition in the intimate nature of these pheno mena. As an example of his mode of reason ing upon this subject, and as further evidence that lie was well acquainted with the class of actions which we now call reflex or physical, the following passage from the eleventh sec tion of this essay may be cited :— " The objection against the mind's produ cing the vital motions, drawn from their being involuntary, must appear extremely weak ; since there are a vanety of motions equally independent upon our will, which yet are cer tainly owing to the mind. Thus, as had been already observed, the contraction of the pupil from light, and the motions of the body from tickling, or the apprehension of it, undoubt edly flow from the mind, notwithstanding their being involuntary. The shutting of the eye lids, when a blow is aimed at the eye, is an other instance of a motion performed by the mind in spite of the will ; for, as the threat ened blow does not, by any corporeal contact, affect the orbicular miiscle of the palpebne, its contraction must necessarily be deduced from the mind, moved to perform this action from the apprehension of something ready to hurt the eye : and if there are some who, by an effort of the will, can restrain this motion of their eyelids, yet this does not proceed so much from the mind's making no attempt, in consequence of the apprehended danger, to close the palpebra!, as from the superior eye lid's being kept up by a strong voluntary con traction of its levator muscle. We cannot, by an effort of the will, either command or re strain the erection of the penis ; yet it is evi dently owing to the mind : for sudden fear, or anything. which fixes our attention strongly and all at once, makes this member quickly subside, though it were ever so fully erected. The titillation, therefore, of the vesicula semi notes by the semen, lascivious thoughts, and other causes, only produce the erection of the penis, as they necessarily excite the mind to determine the blood in greater quantity into its cells." Whytt's view is best explained in the follow ing passage of the same work :—" Upon the whole, there seems to be in man one sentient and intelligent PRINCIPLE, which is equally the source of life, sense, and motion, as of reason ; and which, from the law of its union with the body, exerts more or less of its power and influence as the different circumstances of the several organs actuated by it may require. That this principle operates upon the body, by the intervention of something in the brain or nerves, is, I think, likewise probable; though, as to its particular nature, I presume not to allow myself in any uncertain conjectures ; but, perhaps, by means of this connecting me dium, the various impressions, made on the several parts of the body, either by internal or external causes, are transmitted to and perceived by the mind ; in consequence of which it may determine the nervous influence variously into different organs, and so become the cause of all the vital and involuntary motions as well as of the animal and voluntary. It seems to act necessarily and as a sentient principle only, when its power is excited in causiog the former ; but in producing the latter it acts freely, and both as a sentient and rational agent."' The third fasciculus of the Annotationes Academicm of Geo. Prochaska was pub lished in 1784. It contains the Essay on the Functions of the Nervous System. It is impossible to speak too highly of this profound and accurate dissertation. Although short, it comprehends all the leading facts connected with the working of the nervous system, and affords abundant indications that its author had thought deeply on the subject. I know of no essay, of more modern date, which exhibits the same profound knowledge of nervous pheno mena, and which is equally comprehensive.
How it caine to be so long neglected can only be explained by the too general incompetency of physiologists to appreciate his views. Yet his language is remarkably clear and precise. No one can have done more ample justice to his predecessors and contemporaries. His lite rary research was extensive and accurate, and his historical summary is most interesting and instructive. The attentive perusal of this essay more frequently than once has impressed me strongly with the conviction that Prochaska WaS a inan of the highest mental' capacity and of great power of generalization, and I shall rejoice to see his work made easily accessible to all medical readers.
A brief stimmary of this important work will not be out of place here.
In the first chapter, the first seven sec tions are occupied with an historical account of the views of preceding philosophers, begin ning with Aristotle and Galen. In the eighth section, he remarks, " At length we abandon the Cartesian rnethod of philosophizing in this part of animal physics, and embrace the New tonian, being persuaded that the slow, nay, the most uncertain road to truth is that by hypo thesis and conjecture, but that by far the more certain, more excellent, and the shorter way is that, gum a posteriori ad causam ducit. Newton distinguished the inscrutable cause of the phy sical attractions by the name force of attrac tion ;' he observed its effects, armnged them, and detected the laws of motion, and thus esta blished a useful doctrine, honoumble to human genius. In this way we ought to proceed in the study of the nervous system ; the cause latent in the nervous pulp, which produces certain effects, and which hitherto has not been deter mined, vve shall call vis nervosa ; its observed effects, which are the functions of the nervous system, we shall arrange, and expose their laws, and in this manner we shall be able to construct a true and useful doctrine, gum arti medicm novain lucem et faciem clegantiorem datum est pro certo." Ilaller, he admits, had previously used the term " vis nervosa" to express the power by which nerves cause muscles to con tract, but to Unzer he assigns the credit of having thrown the greatest light upon this sub ject, although he states that to accommodate himself to the times in which he wrote and to make himself more generally understood, he still used the term " animal spirits," although his doctrine was quite independent of such an hypothesis.
In the second chanter Prochaska gives all admirable summary of the leading anatomical characters of the nervous system. His succinct description of the nervous centres is excellent, and shows that he bad anticipated views which long afterwards were put forward as original. Speaking of the crura cerebri, he describes them thus, " dtio magnacrura cerehri, in quilms omnis medulla ab utroque cerebri hemisphwrio collecta videtur." The compound origin of the fifth and spinal nerves and the existence of the ganglion on one of their roots he was well acquainted with. He concludes thus, " However complex be the mechanism of the nervous system, I think it can be divided into three parts, just as the functions themselves are conveniently divi sible into three classes : namely, first, the animal organs, or those associated with the faculty of thinking, these are the bmin and cerebellum ; secondly, the sensorium commune, which con sists of the medulla spinalis and oblongata, not excepting also such part of the medulla of the bmin as gives immediate origin to nerves ; and, thirdly, the nerves properly so called, which are prolonged from the sensorium commune to the whole body." An examination of the comparative anatomy of the nervous system next follows, affording a clear and concise exposition of the existing state of knowledge on that subject.
The question discussed in the succeeding section is, " quid per vim nervosam intelligitur, et qim sint generales ejus proprietates ?" and he affirms the principle of the inherence of the ;its nervosa in the nervous structure itself, and the developement of that force by changes taking place in it. Leaving it to those who devote themselves to the study of experimental physics to inquire into the nature of the nervous force, he endeavours to determine its general proper ties or laws before inquiring into the special functions of the nervous systetn.
1. The first lasv which he lays down is that the vis nervosa requires, for its action, a stimu lus. Here, likewise, he repeats the assertion, that the vis nervosa is an innate property of the nervous medulla—" innata pulpm medullaris proprietas. Sicut scintilla latet in chalybe ac silice, nee prius elicitur, nisi attritus mutuus chalybis, silicisque accesserit : ita vis nervosa latet, nec actiones systematis nervosi prius pro ducit donee stimulo applicito excitatur, quo durante durat, ablato cessat agere, et redeunte iterum reddit." 2. The stimulus necessary for the develope ment of the nervous force is twofold, stimulus corporis and stimulus anima. The former is any body fluid or solid applied externally or internally to the nervous system. The latter is that of the mind, which, through its connection with a part of the nervous system, is capable of influencing, to a certain extent, the rest of that system and through it the body.