THE PRODUCTION OF ACTIVE IMMUNITY 157 



immunity to the living germ obtained through the employ- 

 ment of the residue is apparently much higher than that 

 which follows treatment with the toxic portion. It does 

 not seem improbable that the specific immunizing group 

 which is contained in the residue represents that group of 

 the colon bacillus which is of primary importance in the 

 development of specific acquired immunity to this germ. 

 The work just detailed may be summed up as follows: 



1. Guinea-pigs treated at intervals of from three to 

 four days with intra-abdominal injections of the colon 

 residue acquire an active immunity to at least eight times 

 the ordinary fatal dose of the living bacterium. 



2. The degree of immunity secured does not depend so 

 much upon the amount of the residue or non-poisonous 

 portion that has been injected as upon the number of 

 treatments and the interval of time over which they have 

 been continued. 



3. The length of time over which the immunity continues 

 is rather short in the case of animals that have received a 

 large amount of the residue in a few doses continued over a 

 short period. 



4. Rabbits that received from two to three injections of 

 0.5 gram each of the residue acquire an immunity to 

 quantities of the living bacillus that kill the controls within 

 five hours. 



5. The immunity induced by the colon residue or non- 

 poisonous part is specific, and previous treatments of 

 animals with the residues of egg-white, peptone, and the 

 typhoid bacillus give no immunity to the colon bacillus. 



In continuing this work Vaughan and. Wheeler 1 decided 

 in the first place to ascertain whether or not a single dose 

 of the residue gives any immunity; if so, what degree of 

 immunity does it afford and how long does it continue? 



The number of immunizing doses given in the work 

 already reported ran from three to nine, and the special 

 object of the work here reported is to ascertain the effects 

 of a smaller number of immunizing doses. 



1 New York Med. Jour. June, 29, 1907. 



