24 THEORIES OF IMMUNITY 



To these substances of biologic origin have been added 

 quite recently, several organic compounds obtained synthet- 

 ically and notably substances of the series of arsenobenzenes, 

 either simple or multimetallic, of which the chemical com- 

 position is well defined but of which the constitution is still 

 imperfectly understood. 



The ability or lack of ability to traverse dialyzing mem- 

 branes is the most important distinctive characteristic of 

 these two categories of substances in their reaction on the 

 organism. Those which can traverse membranes rapidly 

 penefrate into the tissues, combining with substances of the 

 organism according to the laws of their chemical affinities 

 and produce immediately or at least very rapidly, effects 

 which are nutritive, exciting, toxic, hypnotic, or anesthetic' 

 according to the nature of the products which they form 

 with the cell contents and according to the role of the cells 

 in the life of the organism. That part which is not fixed by 

 the tissues is quite rapidly eliminated by the kidneys or the 

 intestines. 



On the other "hand the colloids, which do not traverse the 

 cell membranes which enclose each cell, cannot be either 

 assimilated or fixed by the tissues or eliminated without 

 being subjected to a special transformation. The charac- 

 teristic feature which results is the relative delay of the 

 reactions which they provoke in the organism. Furthermore, 

 we must well understand that there are no absolutely sharp 

 distinctions between colloids and crystalloids. 



In setting up a series of more or less permeable dialyzing 

 membranes it is recognized that certain colloids traverse 

 certain membranes which others do not traverse, and that 

 the same membranes may allow one part of one colloid to 

 pass without the other. Thus a given membrane may pass 

 diphtheria toxin more easily than antitoxin and the toxin 

 will be only partially eliminated or dialyxed. We must 

 necessarily conclude that all colloids, from the point of view 

 of the size of the granules of which they are composed are 

 not identical, that a colloid is not absolutely homogeneous 

 in all its parts, that it is composed of granules larger or smaller, 

 that is to say, of granules containing a larger or smaller 

 number of molecules. 



