PHYSIOLOGY OF THE NERVOUS SYSTEM. 
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 magnacrura cerebri, inquibus omnis 
medulla ab utroque cerebri hemispherio 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 brain 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 
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 que sint generales 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- 
Here, likewise, he repeats the assertion, 
that the vis nervosa is an innate property of the 
nervous medulla—“ innata pulpe 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 anime. 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 systein 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, 
721b 
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 more 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 absque cere- 
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 fcetus, 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 of 
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 corporeal sense without concomitant per- 
ception. And he shows that this power is-in- 
222 HOEK 
