THE PRODUCTION OF ACTIVE IMMUNITY 155 



TABLE XIII 



1 c.c. OF A 16-HOUR CULTURE OF COLON BACILLUS KILLED CONTROLS 

 IN TWENTY-FOUR HOURS, i c.c. DID NOT KILL 



Peptone Residue 



From the above tables it can be readily seen that the 

 residues obtained from the peptone and albumin possess 

 little if any immunizing properties against infection with 

 the colon bacillus. In the case of the animals treated with 

 the peptone residue, the first three pigs received a different 

 residue from that given 'to the remainder. This residue 

 had been thoroughly extracted with' alkaline alcohol, and 

 was evidently possessed of no immunizing properties what- 

 ever. On the other hand, the residue which was received 

 by pigs No. 4 to No. 8 inclusive had not been subjected to 

 so thorough an extraction. It is therefore highly probable 

 that the slight degree of immunity apparently obtained 

 in some of the latter animals was due to the presence of 



