720v 



PHYSIOLOGY OF THE NERVOUS SYSTEM. 



the left side.* A longitudinal section of the 

 cord along the median line in frogs does not 

 cause paralysis ; it gives rise, however, to a 

 temporary disturbance of the functions of the 

 cord which soon subsides.f 



Continuity of the spinal cord and encepha- 

 lon is then the condition necessary to establish 

 the control of the former organ over the volun- 

 tary movements and sensations of the trunk. 

 The disunion of the cord or any portion of it 

 from the encephalon dissociates the cord or 

 the separated segment of it from all participa- 

 tion in mental nervous actions. So long as the 

 cord is united with the brain, it takes a certain 

 share in mental nervous actions, in acts of sen- 

 sation and volition; this, however, it loses 

 when disease or accident separates the one from 

 the other. 



It is plain, then, that the spinal cord, although 

 apart from the encephalon it takes no share 

 in sensations and voluntary actions, (for then, 

 indeed, these phenomena cannot take place as 

 far as regards the trunk and extremities,) while 

 united with the encephalon participates fully 

 in sensori-volitional actions, and its integrity 

 is quite necessary to the perfection of those 

 actions. 



1 repeat that we are not justified in supposing 

 that the mind localises itself exclusively in some 

 or all of the gangliform bodies, the assemblage 

 of which constitutes the encephalon ; but this we 

 may assert, with perfect justice, that when the 

 cord has been separated from the encephalon, 

 the mind appears as it were to cling to the 

 latter organ, and to lose all its connection with 

 the former. 



Does then the cord, under these circum- 

 stances, lose all its power ? Does it, when sepa- 

 rate from the encephalon, shew no indication 

 of acting as a nervous centre ? Undoubtedly 

 it does show abundant indications. A series 

 of actions, which had attracted the notice of 

 several physiologists, are still capable of being 

 developed through the instrumentality of the 

 whole cord or of any portion of it, the nerves 

 of which may remain uninjured both as to their 

 central and peripheral connections. 



Phenomena of this nature may be produced 

 in all vertebrate animals. They are, however, 

 especially marked in the cold-blooded classes, 

 in consequence of the more enduring character 

 of the nervous force in those creatures than in 

 the warm-blooded. Hence frogs, salamanders, 

 snakes, turtles, fishes, have been generally 

 selected by physiologists for exhibiting these 

 phenomena. In the young of warm-blooded 

 animals they are more manifest than in adults 

 of the same class. 



If a frog be pithed by dividing the line of 

 junction of the medulla oblongata with the 

 spinal cord, the following effects may be ob- 

 served. After the first disturbance, general 

 convulsions, &c., consequent upon the division 

 of the cord, the animal, if placed on a table, 

 will assume his ordinary position of rest. In 

 some cases, however, frequent combined move- 

 ments, much resembling acts of volition, will 



* Med. Chir. Trans, vol. i. p. 200. 



t See Flourens' Experiments, Syst. Nerveux. 



take place for a longer or shorter time after 

 the operation. When all such disturbance 

 has ceased the animal remains perfectly still 

 and as if in repose, nor does it exhibit the 

 slightest appearance or give the least expres- 

 sion of pain or suffering. It is quite unable 

 to produce any spontaneous or voluntary move- 

 ment of parts supplied with nerves from be- 

 low the section, that is, of the trunk or extre- 

 mities. However one may try to frighten it, 

 it remains in the same place and posture. 

 The only appearance of voluntary motion is the 

 winking of the eyelids, which, however, proba- 

 bly is not excited by the will. If, now, a toe be 

 pinched, instantly the limb is drawn up, or the 

 animal seems to push away the irritating agent, 

 and then draws up the leg again into its old 

 position. Sometimes a stimulus of this kind 

 excites both legs, and causes them to be thrown 

 violently backwards. A similar movement al- 

 most constantly follows stimulation of the anus. 

 If the skin be pinched at any part, some 

 neighbouring muscle or muscles will be thrown 

 into action. Irritation of the anterior extre- 

 mities will occasion movements of them ; but 

 it is worthy of note that these movements are 

 seldom so energetic as those of the posterior 

 extremities. 



We may remark here, that phenomena of 

 this kind are not confined to the trunk and 

 extremities, which are supplied only by spinal 

 nerves. The head and face, with which the 

 encephalon remains in connection, exhibit 

 similar actions. The slightest touch to the 

 margin of either eyelid or to the surface of 

 the conjunctiva causes instantaneous winking; 

 the attempt to depress the lower jaw for the 

 purpose of opening the mouth is resisted ; and 

 the act of deglutition is provoked by applying 

 a mechanical stimulus to the back of the 

 throat.* 



Actions similar to those which take place in 

 the decapitated frog, occur in the human subject 

 when the spinal cord has been separated from 

 its encephalic connections by disease or acci- 

 dent. In such cases it is found that although the 

 will cannot move the paralysed parts, the lower 

 extremities for instance, movements do occur 



* Sir Gilbert Blane, in his admirable Croonian 

 Lecture on muscular motion, having drawn the dis- 

 tinction between instinctive and voluntary actions, 

 makes the following remarks. " There are facts 

 which show that instinctive actions, even in ani- 

 mals endowed with biain and nerves, do not de- 

 pend on sensation. I took a live kitten, a few days 

 old, and divided the spinal marrow by cutting it 

 across at the neck. The hind paws being then irri- 

 tated by pricking them, and by touching them with 

 a hot wire, the muscles belonging to the posterior 

 extremities were thrown into contraction, so as to 

 produce the motion of shrinking from the injury. 

 The same effects were observed in another kitten 

 after the head was entirely separated from the 

 body." And again, " In an acephalous monster, 

 the like phenomena were observable. Jt moved up 

 its knees, when the soles of its feet were tickled ; 

 it performed the act of suction ; passed urine and 

 feces; and swallowed food." * * * " The like 

 takes place with regard to insects ; for, after the 

 head of a bee is separated from the body, the 

 hinder part will sting, xipon the application of such 

 a stimulus as would excite the same action in the 

 animal in a perfect state." 



