PHYSIOLOGY OF THE NERVOUS SYSTEM. 



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admirable summary of the leading anatomical 

 characters of the nervous system. His succinct 

 description of the nervous centres is excellent, 

 and shows that he had anticipated views which 

 long- afterwards were put forward as original. 

 Speaking of the crura cerebri, he describes them 

 thus, " duo magna crura cerehri,inquibus omnis 

 medulla ab utroque cerebri hemispheric col lecta 

 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 brain and cerebellum ; 

 secondly, the sensor ium commune, which con- 

 sists of the medulla spinalis and oblongata, not 

 excepting also such part of the medulla of the 

 brain 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 quae sintgenerales ejus proprietates ? " and he 

 affirms the principle of the inherence of the vis 

 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 system. 



1. The first law 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 pulpae medullaris 

 proprietas. Sicut scintilla latet in chalybe ac 

 silice, nee prius elicitur, nisi attritus mutuus 

 chalybis, silicisque accesserit: ita vis nervosa 

 latet, nee 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 animiE. 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. 



3. The vigour of the nervous actions bears a 

 direct relation to that of the nervous force and 

 to the power of the exciting stimulus. The 

 actions of the nervous system will be greater 

 and more vigorous in proportion as the vis ner- 

 vosa may be more active (mobilior) and the 

 stimulus more efficacious ; on the other hand, 



the nervous force will be more sluggish and 

 the stimulus less effective, where the nervous 

 actions are more languid. A less stimulus is 

 sufficient for a more active vis nervosa, as the 

 application of a stronger stimulus may com- 

 pensate for a more sluggish vis nervosa, yet an 

 equal effect may be produced in the nervous 

 actions. The nervous force, however, is not 

 equally susceptible to every kind of stimulus ; 

 sometimes it obeys one moie than another, 

 although both may appear equally powerful : 

 nay, sometimes it experiences a more powerful 

 effect from the stimulus which may seem the 

 mildest. According to Haller, the heart and 

 intestines are more powerfully stimulated to 

 contract by air blown into them than by water 

 or by any poison ; on the contrary, a drop of 

 water let fall into the trachea excites violent 

 cough, whereas air passes through it in breath- 

 ing as if unfelt by it. 



4. The nervous force is augmented by va- 

 rious circumstances. Among these he enume- 

 rates age at an early age the vis nervosa being- 

 greater than at a more advanced period of life 

 climate, and disease. 



5. On the other hand, the vis nervosa may 

 be depressed or diminished by all causes which 

 depress the powers of life, by the direct appli- 

 cation of opium and other sedatives to the 

 nervous matter. 



6. " Vis nervosa est divisibilis et absquecere- 

 bro in nervis subsistit." In illustration of this 

 law he adduces the instances of nerves remain- 

 ing excitable after they have been separated 

 from the cord or from the brain ; also the exci- 

 tability of paralytic limbs by the electrical 

 stimulus. And, he states, the vis nervosa not 

 only remains fora long time in the spinal cord 

 and nerves which have been separated from the 

 brain, but even in nerves which never had any 

 connection with the brain, as is shown by the 

 acephalous fetus, which, without a brain, and 

 by the sole force of the nerves and medulla 

 spinalis, if this be not deficient, lives the full 

 time in the uterus of the mother, is nourished, 

 grows, and, when it comes into the light, shows 

 often no obscure signs of life. To this law he 

 attributes the persistence of the rhythmical ac- 

 tion of the heart after the decapitation of ani- 

 mals. 



7. Idiosyncrasy is a peculiar affection of the 

 nervous force. Among the examples of idio- 

 syncrasy he enumerates, fainting at the sight of 

 blood, the uneasiness and even terror produced 

 in some persons by the exhalations from a cat, 

 which may be in the same room, although un- 

 seen ; fainting from the perception of particular 

 odours. 



In his third chapter Prochaska proceeds to 

 examine the functions of nerves. He describes 

 the mode of action of nerves, their power of 

 receiving impressions with great facility, and ofV 

 propagating them with the greatest velocity 

 either to the centre or to the periphery. This 

 power he calls the vis nervosa of nerves, which 

 also may be called the sensibility or mobility 

 of nerves, and to which Unzer had given the 

 name rorpnreal sense without concomitant per- 

 ception. And he shows that this power is in- 



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