186 ON VARIABILITY AND ADAPTATION 



class of substances possessing an intermediate state in which 

 they are present in the form of fluid or of ductile crystals. 



This in itself, while a matter of interest, would not perhaps 

 be of great importance were it not that associated with this 

 property, as pointed out by Schenck, is a further one which we 

 are led to regard as of great significance. Schenck has called 

 attention to the fact that whereas ordinary crystalline sub- 

 stances permit of mixture with other substances to a very limited 

 degree, all the members of this class, even when of widely different 

 chemical composition, unite in all proportions, the melting- 

 point of the mixture being then determined by the relative 

 amounts of the two substances present. If, then, we admit 

 that more than one substance present in the organism belongs 

 to this class, it is by no means assured that a given doubly re- 

 fractive sphero-crystal (in the adrenal, for example) is com- 

 posed of a single substance. It may be an admixture of two 

 or more. Nor is this everything. Their power of mixing 

 with and absorbing 1 other substances is very great, not to say 

 extraordinary. With water, for example, the oleates, the 

 lecithins, protagon, and allied bodies do not in the first place 

 dissolve. They absorb it and swell up. Only after they have 

 swollen up greatly does solution, or what appears to corre- 

 spond to solution, show itself, for there is still debate among 

 the physicists regarding the solubility of these bodies. What 

 is true of water is true of a large number of other substances ; 

 oleic acid, for example, and neutral fats are absorbed, and 

 within certain limits, despite the presence of these foreign sub- 

 stances, the globules continue to exhibit double refraction. 

 Such admixture, for example, occurs in the adrenal. Studying 

 the adrenal juice under the polarizing microscope, one of the 

 earliest facts that strike the observer is that the globules are 

 of varying lustre, some bright and clear, others pale, others 

 faint, just discernible shadows. And, in addition, one finds 

 aberrant globules. Fig. 2, Plate IV. shows some of the forms I 

 have seen. 



Remembering that these lipoid myelins are widely distributed 



through the organism, this power of admixture and absorption 



appears to be most significant. To this Albrecht has already 



called attention in connexion with the abundant myelin of 



1 [Or in modern parlance " adsorbing."] 



