228 INFECTION AND RESISTANCE 



bacteria are repeatedly passed through the bodies of animals, and, 

 indeed, alterations of virulence signify biologically a process of 

 adaptation on the part of the bacteria just as increased immunity 

 indicates a similar process on the part of the invaded subject. 



This lessened susceptibility to antibodies is noticeable not only in 

 strains cultivated from the body in disease, but can be produced arti- 

 ficially by cultivating the bacteria in inactivated homologous immune 

 serum. This has been accomplished by Walker 29 especially, and by 

 Miiller, 30 with both typhoid bacilli and cholera spirilla cultivated 

 apon broth mixed with serum. Such strains not only increase 

 in virulence but lose in both agglutinability and susceptibility to 

 bactericidal effects. Sacqueppee 31 obtained similar results by keep- 

 ing the organisms in collodium sacs in the peritoneal cavity, and 

 Bail 32 found similar inagglutinability of typhoid bacilli taken from 

 the peritoneal exudates of guinea pigs dead of infection. 



Zinsser and Dwyer 33 have noticed similar inagglutinability in 

 typhoid bacilli recovered from the peritoneal cavities of guinea pigs 

 injected with anaphylatoxin and bacteria. The anaphylatoxin in 

 these cases possessed distinct aggressive action, and the conditions 

 here were probably very similar to those observed by Bail. 



There are various possible explanations, the most prevalent ones 

 all representing variations of the opinion that such inagglutinable 

 strains possess an inadequate receptor apparatus. Cole 34 advances 

 this because he found these cultures possessed less power to absorb 

 agglutinin than others, and, injected into animals, produced sera 

 which were not highly agglutinating for the injected strain. Some 

 of Cole's experiments show clearly the variable agglutinability dis- 

 played by different strains of the same species. Thus the agglutina- 

 tion in the same serum 



Of strain E = 1:8,000 



Of strain H = 1:7,000 



Of strain I = 1:4,500 



Of strain W = 1:4,500 



Of strain C = 1:4,000 



The difference here between E and C actually amounted to a 

 Telation of 1 to 2. A rabbit immunized with strain I furnished a 

 serum which agglutinated strain E more powerfully than I itself. 



Miiller' s experiments have the same general significance. It has 

 ;also been suggested that the inagglutinable bacteria, especially those 

 .from the peritoneal exudate, which Bail found were neither agglu- 



29 Walker. Journ. of Path, and Pact., Vol. 8, 1902. 



30 Miiller. Munch, med. Woch., 1903. 



31 Sacqueppee. Ann. Past., Vol. 4, 1901. 



32 Bail. ArcMv f. Hyg., Vol. 42. 



33 Zinsser and Dwyer. Proc. Soc. for Exp. Biol and Med., Feb., 1914. 



34 Cole. Zeitschr. f. Hyg., Vol. 46, 1904. 



