144 PROTEIN POISONS 



been reached in each case, and within from ten to twelve 

 hours it has again returned to normal. The similarity of 

 the symptoms in the two instances leads us to believe that 

 in all probability we are here dealing with an immunity 

 which is identical in character with that which is usually 

 spoken of as natural immunity. This idea has been further 

 upheld by the fact that we have been able to obtain from 

 egg albumen and peptone poisonous substances which 

 resemble the toxic portion of the colon bacillus in their 

 action, and by the injection of single non-fatal doses of 

 which it is possible to obtain the same transitory immunity 

 to the living colon germ as is observed after the injection 

 of the colon poison. That this toxic group is common to 

 certain bacteria and other protein bodies is not improbable, 

 and this would furnish an explanation not only of the 

 increased resistance to certain bacterial infections occurring 

 in animals treated with albumin and peptone, but of some 

 phases of natural immunity as well. However, this subject 

 will be more fully considered in a future paper on a compari- 

 son of these various poisons. It may be well to reiterate 

 at this point that we have conclusively shown that the 

 poison which we have been able to obtain from the colon 

 bacillus, and to which death is due in colon infection, 

 does not come directly from the peptone or albumen in 

 the culture medium, since we have obtained the same 

 poison from the bacillus when grown upon a protein-free 

 medium. 



2. Immunization with the Residue Remaining after the 

 Extraction of the Poison from the Colon Bacillus. The residue 

 remaining after the extraction of the poison from the 

 colon bacillus, which is insoluble in alkaline absolute alcohol, 

 is soluble in water. The resulting solution is, however, 

 quite decidedly alkaline in reaction, owing to the presence 

 of free alkali. Since it is essential that we should avoid 

 the irritative effects which would follow the injection of 

 this free alkali into the peritoneal cavity, the solution is 

 first rendered slightly acid with hydrochloric acid, and 

 then neutralized with sodium bicarbonate before injection. 



