EFFECTS OF EXPERIMENTAL LESIONS 839 



also it will be noted that after section of the posterior roots of one side, 

 the corresponding limb hangs lower than its fellow because its muscles 

 are toneless. 



Stimulation of the central end of a cut afferent root produces, as has 

 already been indicated, a contraction of the muscles accompanied by a 

 reciprocal inhibition of their antagonists, so that some definite move- 

 ment of the joint takes place. This movement is, hoAvever, merely a 

 flexion or extension or rotation, but with no very evident object in view. 

 In this regard it is quite different from the purposeful movement which 

 results from stimulation of a skin area, indicating, therefore, that the 

 receptor apparatus itself must contribute to the nerve impulse some- 

 thing which causes it to bring about a more perfectly integrated move- 

 ment of the musculature than is the case when the nerve trunk is di- 

 rectly stimulated. 



Besides the movements of the musculature innervated from segments 

 which are. beside those of the stimulated afferent root, there is a general 

 reflex 'response through other centers, for example, the respiratory and 

 the vasomotor; and, in animals which are not deeply anesthetized, there 

 is also evidence of pain. Stimulation of the peripheral end of the sen- 

 sory root has of course no effect. 



THE SPINAL CORD AND BRAIN STEM 



The results of transsection of the cord have been already sufficiently de- 

 scribed. It remains to discuss the effect of total ablation or removal of 

 portions of the cord. As would be expected, there is a marked degree 

 of shock for some weeks after ablation. During this shock the tone 

 of the sphincters and vessels is greatly depressed, so that congestion 

 and edema of the feet, diarrhea and retentio urinag are marked, and 

 ulceration of the skin is practically unavoidable. After a few weeks, 

 however, recovery becomes evident in so far as the blood vessels and 

 sphincters are concerned, but the skeletal musculature atrophies very 

 extensively and comes to resemble connective tissue. If the spinal 

 ablation involves the thoracic region, for example, the affected in- 

 tercostal muscles become stiff and parchment-like; the bones also get 

 brittle, and visible perspiration can not be produced. On the other 

 hand, after some time the sphincters functionate more or less normally, 

 the hair is shed and renewed in normal fashion, and the application of 

 cold to the skin causes the usual vascular reaction. It is of interest 

 that in female animals whose lumbar spinal cord has been removed, 

 pregnancy may take place normally, followed by lactation. 



Section Just Above the Medulla, After such an operation, the ani- 



