542 THE POSTERIOR PITUITARY AND THE NERVOUS SYSTEM. 



within the latter must be more or less a continuation of that 

 in the hlood-vessels. Again, we have suggested that the blood- 

 plasma, including its oxidizing substance, was the liquid in the 

 axis-cylinders; that this is true is shown by Ehrlich's observa- 

 tion that "the conditions in the nerve-structures essential to 

 the methylene-blue reaction" were, he thought (1886): "(1) 

 oxygen saturation; (2) alkalinity." We have shown that these 

 are the essential attributes of blood-plasma. 



Fio. 2. SENSORY NERVE-ENDINQ STAINED WITH 

 (METHOD OP EHRLICH) IN THE EXOCARDIUM OF THE LEFT AURICLE 

 OF A GRAY RAT. (After Smirnow.) 



This seems to us to afford an insight into the physiological 

 chemistry of the axis-cylinder of the neuraxon when a short 

 distance below the latter it has become a medullated nerve. 

 Indeed, the prevailing view that the myelin represents a pro- 

 tective and insulating coat may at least be said to be open to 

 doubt, especially when coupled with the facts that its chemical 

 composition is unknown, and that there is another external coat: 

 the neuro-keratin neurilemma, which suggests, by its composi- 

 tion, that it is an isolating covering and that it also fulfills this 



