404 THE NERVOUS SYSTEM. 



wounds of peripheral nerves, are also reflex. The tetanic spasm is 

 usually, if not always, excited by an external cause ; and this cause 

 may be so slight that in the healthy condition it would have no per- 

 ceptible effect. The accidental movement of the bedclothes, the shut- 

 ting of a door, the passing of a carriage in the street, or even a current 

 of air upon the skin, may be sufficient to throw the muscular system 

 into spasmodic action. The irritability of the spinal cord as a nervous 

 centre is, therefore, liable to be increased or diminished by causes acting 

 upon it from without. 



Reflex Action of the Cord in Warm-blooded Animals and in Man. 

 In the frog and other cold-blooded animals, the reflex action of the 

 spinal cord lasts for a considerable time after death ; often continuing, 

 if the animal be kept in repose and sufficiently cool and moist, for 

 twenty-four hours or longer. In the warm-blooded animals, it disap- 

 pears more rapidly ; and it must be sought for, if at all, within a short 

 time after death, since a nearly constant supply of blood is essential 

 in these animals to the irritability of the nervous system. But if the 

 circulation be maintained by means of artificial respiration, the reflex 

 action of the cord will continue, independently of the brain; and 

 although sensation and volition are absent, movements of the leg may 

 be produced by pinching the skin of the foot. 



Kobin* has observed the reflex action of the spinal cord, after de- 

 capitation, in man, in the case of an executed criminal whose body 

 was subjected to examination. The muscular contractions were pro- 

 duced about one hour after execution. " While the right arm was 

 lying extended by the side, with the hand about 25 centimetres dis- 

 tant from the upper part of the thigh, I scratched with the point of a 

 scalpel the skin of the chest at the areola of the nipple, for a space 

 of 10 or 11 centimetres in extent, without making any pressure on 

 the subjacent muscles. We immediately saw a rapid and successive 

 contraction of the great pectoral muscle, the biceps, probably the 

 brachialis anticus, and lastly the muscles covering the internal con- 

 dyle. 



" The result was a movement by which the whole arm was made to 

 approach the trunk, with rotation inward and half-flexion of the fore- 

 arm upon the arm; a true defensive movement, which brought the hand 

 toward the chest as far as the pit of the stomach. Neither the thumb, 

 which was partially bent toward the palm of the hand, nor the fingers, 

 which were half bent over the thumb, presented any movements. 



" The arm being replaced in its former position, we saw it again 

 execute a similar movement on scratching the skin, in the same manner 

 as before, a little below the clavicle. This experiment succeeded four 

 times, but each time the movement was less extensive ; and at last 

 scratching the skin over the chest produced only contractions in the 

 great pectoral muscle which hardly stirred the limb." 



Journal de TAnatoinie et de la Physiologie. Paris, 1869, p. 90. 



