VASCULARITY IN THE NERVOUS SYSTEM 455 



The nourishment of the nerve fibers, according to what seems 

 to be the fairly generally accepted view, is derived very largely, 

 if not entirely, from the cell body. Tt is difficult to believe, 

 however, that a fiber a meter long can be nourished entirely 

 by the activity of a single cell body situated at one end of it, 

 though the ordinary conception of the functions of the nucleus 

 would lead one to expect metabolism as a whole to be more 

 rapid, and perhaps more important in some respects, in that 

 part of the neurone which contains it. Certain authors state 

 that the myelin sheath is concerned in the nutrition of the axone, 

 and if this be true, it is easy to see that myelination may enable 

 a tract to carry on its functions satisfactorily with a much poorer 

 blood supply than would otherwise be needed, if activity is not 

 constant. The arguments in favor of this view are summed up 

 by Mathews ('16). Moreover, the neuroglia itself may perhaps 

 act as an intermediary between the blood and the nervous ele- 

 ments. Achucarro ('15) attributes to the neuroglia considerable 

 functional activity "as an interstitial gland which acts on the 

 nerve elements and on the blood, contributing by means of special 

 hormones to the endocrinic harmony of the organism." Cajal 

 also believes that the neuroglia bears a nutritive relation to the 

 nerve cells, and acts as a chemical rejuvenator toward them. 



It is to be noted that the susceptibility of the reflex arc to 

 anaemia, lack of oxygen, drugs, etc., is much greater than that 

 of the nerve trunk, which shows that the blood supply is actually 

 of greater direct physiological importance to some part of the 

 neurone which lies in the gray matter than to the axone (Sher- 

 rington, '06). 



The difficulty is perhaps even greater, and the problem is 

 of even more immediate interest, when we come to consider the 

 differences in the vascularity of the various centers of gray matter. 

 If the functional activities of the neurones involve no metabolic 

 changes, and the only chemical processes occurring are those 

 incident to the relatively small amount of assimilation and 

 respiration necessary to maintain passive life, what is the meaning 

 of the fact that, for example, the blood supply of the dorsal 

 cochlear nucleus is from nearly one and a half times to twice as 



THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 31, NO. 5 



