26 IMMUNE SERA 



again be abstracted from these cells by all kinds of 

 solvents, e.g. by shaking out with ether or chloro- 

 form. The point can perhaps be likened to the 

 difference between saccharin and sugar. Both sub- 

 stances taste sweet, but despite this similarity in 

 their physiological action they behave very dif- 

 ferently toward the cells of the organism. Sac- 

 charin simply passes through the organism without 

 entering into a firm combination, i.e. without being 

 assimilated, and is therefore no food. Its sweeten- 

 ing action is a mere contact effect on the cells 

 sensitive to taste. Sugar, on the contrary, is 

 actually bound by the cells, assimilated and burnt, 

 and so is a true food. Until recently it was believed 

 that the simpler chemical substances could not 

 excite the production of antibodies. Ford and 

 Abel 1 have however been able to show that toad 

 stool poison, a true toxin, against which an anti- 

 toxin can be produced is chemically a glucoside. 



As we shall subsequently see it is possible to 

 immunize the animal body against a large number 

 of substances, including not only such cell products 

 as ferments, toxins and venoms, but also cells of 

 the greatest variety, bacteria, dissolved proteids, etc. 

 All these substances, therefore, must possess hapto- 

 phore groups able to combine with the side chains 

 or receptors in the animal body. Collectively, 

 we speak of such substances as antigens or haptins. 

 1 Ford and Abel, Journal of Biological Chemistry, Vol. ii, 1907. 



