THE NUTRITION OF NERVOUS TISSUE 853 



gen-carrying power of the blood which follows the inhalation of carbon 

 monoxide. Similar mental disturbances may result for a similar reason 

 in pernicious anemia. 



A prolonged condition of low blood pressure may result in the failure 

 of the medullary centers because of the insufficiency of the blood supply. 

 This is perhaps one of the limiting factors in the resuscitation of patients 

 suffering from low blood pressure induced by hemorrhage or secondary 

 traumatic shock. Bayliss has found that if the blood pressure of the 

 cat is maintained at a low level for an hour or two the vasomotor center 

 loses its reflex excitability and the respiratory center fails to maintain 

 a ventilation of the lungs sufficient to support life. Restoration of the 

 blood pressure by transfusion may come too late to cause these centers 

 to recover. In the cat the respiratory center loses its power of revival 

 before the vasomotor center, but the relative susceptibility no doubt 

 varies in different species of animals. The cells of the outlying ganglia 

 of the sympathetic system and, particularly, those of the myenteric 

 plexus are able to withstand a prolonged disturbance in their blood sup- 

 ply much better than the neurons of the central nervous system. For 

 this reason a strangulated loop of intestine which appears hopelessly 

 damaged, by the prolonged circulatory statis to which it has been sub- 

 jected, may recover its normal function with remarkable success. 8 



A close relation probably exists between the distribution of the cap- 

 illaries in the nervous system and the nutritional requirements of its 

 various parts. Measurements indicate that the grey matter, in which the 

 nerve cell bodies lie, is much more richly supplied with capillaries than 

 the white matter. The grey matter is more adequately supplied in the 

 medulla than in the cord, and the same relation holds true between the 

 white matter in these regions. Among the nuclei of the medulla it 

 appears that sensory nuclei are, in general, more richly vascularized than 

 motor nuclei. This relation is perhaps explained by the almost con- 

 tinuous activity of the sensory neurons as contrasted with the more inter- 

 mittent activity of the neurons concerned with motor acts. 



