138 PROTEIN POISONS 



It is a well-known fact that animals which have been 

 treated with non-fatal doses of either the living or dead 

 colon germ acquire a certain degree of immunity toward 

 subsequent infection with this bacillus. If, now, our theory 

 as regards the action of this bacillus is correct, one would 

 suppose that among the groups which we have been able 

 to split off there exist certain ones which possess the power 

 of producing immunity when injected into susceptible 

 animals. To ascertain whether such an active immunity 

 can be established in animals through treatment with the 

 split products of the colon bacillus is the aim of this chapter, 

 and we shall find it convenient to take up (1) the active 

 immunity obtained with the toxic portion, and (2) the 

 immunity obtained with the residue which remains after 

 the separation of the poisonous portion from the cellular 

 substance. 



1. Immunization with the Poisonous Portion of the Cellular 

 Substance of the Colon Bacillus. From the description of 

 the action of the "crude soluble poison" of the colon bacillus 

 given in the preceding chapter, it can be readily seen that 

 the poison with which we are working is one which exerts 

 its action with great rapidity. The difficulties of immunizing 

 animals with such a poison can be readily appreciated, and 

 it is inevitable that during the course of treatment a large 

 number should be lost. Up to the present time our attempts 

 to produce immunity with the toxic portion have been 

 largely confined to intraperitoneal and subcutaneous injec- 

 tions with what we have termed the free or uncombined 

 poison. However, as has been shown in a previous chapter, 

 it is possible to make use of this poison in a combined state 

 by rendering the solution of the toxic part decidedly alka- 

 line with sodium bicarbonate and allowing it to stand for 

 some time, preferably at incubator temperature. With 

 this combined poison, one is able to give much larger doses 

 without producing a fatal result, and, moreover, the effect 

 of the poison is in this instance manifested over a much 

 longer period of time. These two factors are, of course, of 

 primary importance in the production of immunity and it 



