VASCULARITY IN THE NERVOUS SYSTEM 437 



Wiggers ('05, '07, '08) and Weber ('08), on the other hand, 

 maintain that they have definite physiological evidence that the 

 cerebral vessels are under nervous control, and in a recent paper 

 (Orr and Rows, '18) a whole theory of the nature of certain lesions 

 of the central nervous system is based upon the principle that 

 the caliber of vessels entering from the pia mater is regulated 

 by the sympathetic. This would further complicate the problem 

 of injection, the effect of the injection mass and of the various 

 experimental conditions upon the vasomotor mechanism being 

 problematical. The earlier studies of Roy and Sherrington ('90), 

 moreover, led them to conclude that "the chemical products 

 of cerebral metabolism contained in the lymph which bathes 

 the walls of the arterioles of the brain can cause variations of 

 the caliber of the cerebral vessels," though no evidence of vaso- 

 motor control was obtained. If this is so, then it is at least 

 possible that the injection mass may act directly on the walls 

 of the vessels, causing them to change their diameter, and may 

 even cause a different amount of change in the vessels of different 

 regions. The most recent contribution to this problem is that 

 of Weed and McKibben ('19), who seem to have good ground 

 for their conclusion that "The Monro-Kellie doctrine-' then 

 requires marked modification. . . . The cranial cavity is 

 relatively fixed in volume and is completely filled by brain, 

 cerebrospinal fluid, and blood; variations in any one of the three 

 elements may occur, compensation being afforded by alteration 

 in the volume of one or both of the remaining elements." 



It might be thought that if the quantity of blood in the brain 

 is constant when enclosed in the cranium, as maintained by Hill, 

 an injection in this state would yield an absolute quantitative 

 result. This does not appear to be the case, however. It is 

 difficult to be quite sure that there is absolutely no leakage from 

 the ligatured neck before the gelatin sets. Also the quantity 

 of the injection mass remaining in the capillaries will vary with 

 the varying distribution of the total amount of fluid within the 

 cranium. The venous sinuses were always found to be largely 

 filled with the mass, and it might have been expected that the 



3 I.e., that the volume of blood in the brain is constant. 



