THE PARTIAL-FUNCTIONS OF CELLS. 685 



To begin, it was necessary to determine in what manner the 

 trypanosome antibodies affected the parasites. Corresponding to 

 our previous knowledge of immunity we could assume that these 

 antibodies exert a direct poisonous action, i. e., that they therefore 

 probably contained toxophore or trypanolytic groups, so that the 

 anchoring of the antibody by the parasite is followed by an injury 

 or even the destruction of the latter. This, however, is not the case. 

 In contrast to the ordinary strains of trypanosomes, which possess 

 only a uniform group, A, B, or C, and which may therefore be termed 

 "Unios," one meets with other strains which possess two groups in 

 their protoplasm, A and B, and which may therefore be termed 

 "Binios." If such a binio "A-B" is acted on by the isolated 

 antibody A or B, growth will not be injured in the least. Not until 

 both antibodies act at once does this occur. From this it follows 

 that the presence of the antibodies does not produce a direct toxic 

 effect on the parasites. To us it seems that this three-fold experi- 

 ment demonstrates that the antibody acts merely by blocking the 

 food supply by occupying the corresponding receptors. It thus 

 comes to pass that when in the binio A-B the group A is occupied 

 by an antibody, the parasite can continue to vegetate by means of 

 the group B. From this it also follows that groups A and B are 

 essentially nutri-receptors. 



If the amount of antibody is very large, the parasite finds it 

 impossible to obtain nourishment, and consequently dies off. This 

 can easily be demonstrated by mixing the parasite in a test tube with 

 varying amounts of antiserum; the parasite is killed in the high 

 concentrations which completely shut off the food supply, while in 

 the weaker concentrations, which permit a vita minima, the parasites 

 undergo the alteration already discussed, and give rise to a relapse 

 strain. This mutation is therefore referable entirely to a hunger 

 of the protoplasm, and under this influence the trypanosome de- 

 velops new potentialities. I have given the name "atrepsins" to 

 antibodies of the type just discussed, i. e., those whose action is 

 purely antinutritive, and I believe that they play an important role 

 not only with bacteria but in biology in general. 



In view of the fact that the presence of antibodies demonstrates 

 the existence of definite chemical groupings, most of the workers in 

 immunity will have no difficulty in. accepting the idea that there are 

 definite chemical groups in the cell designed for the taking up of 

 nutritive material. A much more difficult question is as to the 



