THE SPINAL CORD 543 



In warm-blooded animals, e.g., cats and dogs, similar results may be 

 obtained for a period of ten hours after division of the cord, about 4 mm. 

 behind the calamus scrip torius, providing artificial respiration is main- 

 tained and the circulation of the blood continued. The cord will then 

 retain its irritability for some time. 



Another and perhaps a more satisfactory procedure is to divide the 

 spinal cord transversely in the lower cervical region, as thereby respiration 

 is not materially disturbed. The animal passes at once into the condition 

 of shock; all muscles posterior to the section become paralyzed; the blood- 

 pressure falls; and the nerve centers which mediate the movements of 

 urination and defecation become inactive. It the animal is properly 

 cared for, it may survive. If so, the shock passes away in a few days 

 or more; the blood-pressure gradually rises to its former level; the muscles 

 regain their former tone; the reflex action of urination and defecation 

 return, all indicating that the spinal cord nerve-centers are again active. 

 In a varying length of time, two or three months, coordinated muscle 

 movements can be executed in response to surface stimulation. Among 

 the reflexes that can be elicited in response to appropriate stimuli may 

 be mentioned the following, viz: 



1 . The Flexor Reflex. This reflex is characterized by a flexion of the 

 thigh and leg, similar to that observed in the frog, when a stimulus such 

 as the prick of a pin is applied to the skin of the foot. The movement 

 is the result of the contraction of the flexor muscles of the thigh and leg. 



2. The Scratch Reflex. This reflex is characterized by a rhythmic 

 alternate movement of flexion and extension of the leg similar to that 

 performed by the animal in scratching the skin for the removal of some 

 irritant. The movement occurs about four times a second and is the 

 result of an alternate contraction of the flexor and extensor muscles of 

 the thigh and leg. The reflex can be elicited by stimulation, mechanic or 

 electric, of an area on the back and sides of the animal behind the shoulders. 



3. The Extensor Thrust. This reflex is characterized by a sudden 

 movement of extension of the thigh and leg, especially if the leg be first 

 somewhat flexed. The movement caused by a sharp contraction of the 

 extensor muscles lasts about 0.2 seconds. It can be elicited by pressure 

 between the plantar cushion and the toe pads. This reflex is sometimes 

 accompanied by flexion of the opposite leg. 



If the conditions of experimentation were favorable, it is quite probable 

 that the human spinal cord would execute similar movements. Thus 

 it was observed by Robin in a man who had been decapitated that reflex 

 muscle contractions could be elicited by stimulating the skin after the 

 laspe of an hour after execution. " While the right arm was lying ex- 

 tended by the side, with the hand about 25 centimeters distant 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 n centimeters in 

 extent, without making any pressure on the subjacent muscles. We im- 

 mediately saw a rapid and successive contraction of the great pectoral 

 muscle, the biceps, probably the brachialis anticus, and lastly the muscles 

 covering the internal condyle. The result was a movement by which the 

 whole arm was made to approach the trunk; with rotation inward and half- 

 flexion of the forearm upon the arm; a true defensive movement, which 



