721E 



PHYSIOLOGY OF THE NERVOUS SYSTEM. 



htrent in ihe medullary pulp of the nerves, and 

 is not simply derived from the brain, but that 

 a certain cohesion of the medullary pulp of 

 the nerves is necessary for the developement 

 of the vis nervosa, because if by compressing 

 a nerve strongly we injure its medulla, so as 

 to disturb the connection of its particles, the 

 nervous force ceases in that part of the com- 

 pressed nerve, nor are impressions propagated 

 further by it, nor if that part of the nerve be 

 stimulated can sensation or motion be pro- 

 duced. 



Although, he says, a nerve is necessary for 

 sense and motion, it is not it alone which feels 

 or moves ; it feels by the brain, which, when an 

 impression made upon a nerve is conveyed to 

 it, represents that impression to the mind; and 

 a nerve causes motion by the muscle when an 

 impression, communicated to the nerve, de- 

 scends to the muscle and excites it to motion. 

 He concludes thus : " Par itaque nervi, in sensu 

 et motu ciendo, est officium, nimirum im- 

 pressionem stimuli recipere, et per totarn suam 

 longitudinem celerrime propagare, qure dum 

 ad cerebrum pervenit, sensus perceptionem 

 causal, dum vero ad musculum, ejus contrac- 

 tionem ciet." 



Prochaska recognises the influence of the 

 nerves upon the bloodvessels, and ascribes va- 

 rious familiar phenomena to this influence, 

 either excited by direct contact of the nerves 

 of the part, or, if the nerves be indirectly 

 affected through the brain (si isti nervi non 

 immediate, sed mediante cerebro afficiantur). 

 Thus he refers to redness of the skin of the 

 face occasioned by exposure to a cold wind, 

 redness of the conjunctiva caused by some irri- 

 tant, erection of the nipple of the breast by 

 titillation, erection of the penis by similar 

 means or through mental emotion, blushing, 

 &.C. He puts forward the notion that the aug- 

 mentation of the nervous force in any part 

 causes an attraction of fluids to that part, as 

 sealing-wax, when rubbed with cloth, becomes 

 electrical and attracts various small particles. 

 To a similar attraction of fluids he ascribes 

 muscular action and many other phenomena, 

 such as the menstrual Mux, the action of the 

 iris, &.c. He also discusses the question whe- 

 ther the nerves have any power over the secre- 

 tions, whether they contribute in any way to 

 the production of animal heat, and how far 

 they are necessary to nutrition. 



The fourth chapter describes the sensorlitm 

 commune, its functions, and its seat. Here it 

 is that Prochaska has put forward his views 

 respecting reflex actions. External impres- 

 sions, which are made upon sensitive nerves, 

 are propagated with great velocity throughout 

 their entire length to their origin, where, (to 

 use his own phrase,) when they have arrived, 

 they are reflected according to a certain law, 

 and pass into certain and responding (certos ac 

 respondentes) motor nerves, by which again 

 being very quickly propagated to muscles they 

 excite certain and determinate movements. This 

 place, he says, in which, as in a centre, nerves 

 of sense and of motion meet and commu- 

 nicate, and in which " the impressions of 



sensitive nerves are reflected into motor nerves," 

 is called, by a term already received by most 

 physiologists, " the sensorium commune." 

 Having referred to the various views of different 

 physiologists as to the seat of the sensorium 

 commune, he expresses his own opinion, that 

 the sensorium commune, properly so called, 

 extends throughout the medulla oblongata, the 

 crura cerebri and cerebelli, a part of the optic 

 thalami, and the entire spinal cord, in a word, 

 as far as the origins of the nerves extend. That 

 the sensorium commune extends to the spinal 

 cord is shown by those movements which con- 

 tinue in animals after decapitation, which can- 

 not be effected without the cooperation of 

 nerves which arise from the spinal cord ; for if 

 a decapitated frog be pricked, not only does it 

 retract the stimulated part, but also it creeps, 

 arid leaps, which could not be done without the 

 consentaneous action (absque consensu) of sen- 

 sitive and motor nerves, the seat of which con- 

 sentaneous action must be in the medulla spi- 

 nalis, siiperstite sensorii communis purte. 



That Prochaska viewed these acts as purely 

 physical in their nature, is apparent from his 

 statement, that they take place under peculiar 

 laws, written, us it were, by nature on the me- 

 dullary pulp of the senaorium. The general 

 law, however, whereby the sensorium com- 

 mune reflects sensorial into motor impressions 

 (itnpressiones sensorias in motorias rerlectit) is 

 our preservation ; so that certain motor impres- 

 sions should succeed to such external impres- 

 sions as might be injurious to our bodies. In 

 illustration he refers to certain acts of this class, 

 such as, irritation of the mucous membrane of 

 the nose creating a violent act of expiration 

 (sneezing) to expel the offending material from 

 the nostril; the spasmodic closure of the glottis 

 when a particle of food or a drop of fluid 

 touches it, or the act of winking excited by 

 the finger being brought close to the eye. 



Prochaska points out that these reflex actions 

 may take place with or without consciousness 

 (vel anima inscia, vel vero anima conscia). In 

 proof of this occurrence without consciousness 

 he refers to certain acts which are observed in 

 apoplectic patients, to the convulsions of epi- 

 lepsy, and to certain actions in profound sleep ; 

 all those actions which occur in decapitated 

 animals he refers to this class, and regards them 

 as being regulated by the remaining portion of 

 the sensorium commune which is seated in the 

 spinal cord. " Omnes istae actiories ex organismo 

 et phi/sicis legibus, sensorio communi propriis, 

 fluunt, suntque, propterea, spontaneee ac au- 

 lomalico;." Actions, however, which the mind 

 directs and moderates by its control, although 

 the sensorium commune may take its share in 

 producing them, may be called animal, and 

 not automatic. 



The second paragraph of this chapter con- 

 tains an excellent discussion of the question, 

 how far the anastomoses of nerves contribute to 

 their mutual action upon each other, or whether 

 that lakes place only through the sensorium 

 commune. On this subject Prochaska adopts the 

 opinions of Whytt, who regarded the nervous 

 centre as essential to these actions, and in the 



