154 PROTEIN POISONS 



Although these experiments are by no means sufficient 

 in extent to warrant the conclusion that the injection of 

 the residue obtained from the colon bacillus furnishes no 

 increased resistance to typhoid infection, it can be seen 

 that the degree of immunity established must be very 

 slight. As far as the typhoid bacillus is concerned, the 

 immunity produced by the colon residue would appear to 

 be specific. If the immunity induced by the colon bacillus 

 is indeed specific, one would suppose that the immunizing 

 group is one which is found only in the residue obtained 

 from the colon germ. 



As has been previously mentioned, we have found it 

 possible by treatment similar to that which we have used 

 in splitting up the colon bacillus to secure toxic substances 

 from egg albumen and peptone, which possess a similar 

 action when injected into the animal body, to that observed 

 after the injection of the colon poison. We have also 

 stated that the same transitory immunity to colon infec- 

 tion followed the injection of the albumin and peptone 

 poison as was obtained with the colon poison itself. The 

 albumen and peptone bear a further resemblance to the 

 bacterial cell substance in that the residue which remains 

 after alcoholic extraction is non-toxic. The question now 

 arose as to whether the injection of the albumen and pep- 

 tone residue afford any immunity to the living colon germ 

 or not. In order to ascertain this point animals were 

 treated with gradually increasing doses of these residues, 

 and subsequently inoculated with the colon bacillus with 

 the following results: 



