24 ACTIVE IMMUNIZATION 



tion. The conceptions therefore of complete or partial parasite as well as of saprophyte 

 are only relative and are dependent upon the bacteria, the animal species, and the mode of 

 infection. 



It is now clear that immunization with living bacteria can 

 Example of on ty ^ e undertaken if the latter belong to the class of half- 

 Active Im- parasites. Pure parasites are excluded from this method, 

 munization As an example of such procedure can be given the immu- 

 with Living Cation of a guinea-pig by intraperitoneal injections with 

 Bacilli. }i v i n g typhoid bacilli. Preliminary to this, the virulence 



of the typhoid culture must be ascertained. 



a. Preliminary test to titrate the virulence of the typhoid culture. 



1. Guinea-pig i./I. 1909 1/20 loopful of typhoid culture intraperitoneal. 



2. /I. active. 



8./I. alive. 



2. Guinea-pig i./I. 1909 i/io loopful of typhoid culture intraperitoneal. 



2. /I. active. 



8./I. alive. 



3. Guinea-pig i./I. 1909 1/8 loopful of typhoid culture intraperitoneal. 



2./I. slightly sick, does not eat. 



3./I. active. 



8./I. alive. 



4. Guinea-pig i./I. 1909 1/6 loopful of typhoid culture intraperitoneal. 



2./I. sick, does not eat, hair raised. 



3./I. still sick. 



4./I. more active. 



8./I. alive. 



5. Guinea-pig i./I. 1909 1/5 loopful of typhoid culture intraperitoneal. 



2. /I. sick, does not eat, hair raised. 



3 ./I. very weak, when placed on side remains so. 



4 ./L f 



6. Guinea-pig i./I. 1909 1/4 loopful of typhoid culture intraperitoneal. 



,./!. f 



From this experiment it becomes evident that the lethal dose of this particular 

 strain of typhoid culture is 1/4 to 1/5 of a loopful for guinea-pigs by intraperitoneal 

 injection. Immunization therefore must be started with a smaller dose e.g., i/io 

 of a loopful. 



b. Immunization. 



1. Guinea-pig 8./I. 1909 i/io loopful of typhoid culture intraperitoneal. 



i6./I. 1/8 loopful of typhoid culture intraperitoneal. . 



2 2. /I. 1/4 loopful of typhoid culture intraperitoneal. 



Animal remains active and healthy. 

 3O./I. i loopful of typhoid culture intraperitoneal. 



5-/II. 2 loopfuls of typhoid culture intraperitoneal. 



Animal remains active and healthy. 



2. Guinea-pig 8. /I. 1909 i/io loopful of typhoid culture intraperitoneal. 



i6./I. 1/4 loopful of typhoid culture intraperitoneal. 



Animal remains active and healthy. 



