156 PROTEIN POISONS 



some of the toxic portion which had been left in the residue 

 as the result of incomplete extraction. In the animals 

 treated with the albumen residue we were unable to obtain 

 any evidence whatever of increased resistance to colon 

 infection. 



It has now been shown that active immunity to the 

 colon germ can be produced in animals by treatment with 

 the split products obtained from this bacillus. This would 

 seem to furnish conclusive evidence that there exist within 

 the colon bacillus certain immunizing groups which are 

 capable of being separated more or less completely from 

 the other constituents of the bacterial cell by means which 

 bring about a chemical cleavage of the latter. Furthermore, 

 it has been seen that the colon bacillus contains at least 

 two different groups, each of which when injected into the 

 animal body is capable of establishing a certain degree of 

 immunity toward subsequent infection with the living 

 germ. One of these groups is contained within the toxic 

 portion, and probably represents a group w r hich is common 

 to many protein bodies, since, as has been shown, it is 

 contained in the poisons secured through the chemical 

 cleavage of egg albumen and peptone, as well as from the 

 colon bacillus. The degree of immunity thus far obtained 

 through the agency of this group is not great. The fact 

 that this group is apparently not specific to the colon 

 bacillus, but can also be obtained from other protein bodies, 

 furnishes an explanation of the increased resistance to 

 infection observed in animals previously treated with 

 solutions of egg albumen and peptone. Again it has been 

 shown that the residue, which, as has been previously 

 stated, is for all practical purposes non-toxic, also contains 

 an immunizing group. The immunizing group contained 

 in the residue differs from that found in the toxic portion 

 in one very important respect. It represents a group 

 which up to the present time we have been able to find 

 only in the colon bacillus, and which when injected into 

 animals affords protection against this bacillus alone. In 

 other words, the immunity produced with the residue is 

 strict!}' specific in character. Moreover, the degree of 



