THE PRODUCTION OF ACTIVE IMMUNITY 139 



is quite possible that with the employment of the combined 

 poison a higher degree of immunization may be obtained. 



That it is possible by means of repeated doses to induce a 

 certain amount of tolerance in animals for the poisonous 

 portion is illustrated in the following tables: 



TABLE VII 



20 MG. OF THIS POISON INVARIABLY CAUSED DEATH IN UNTREATED PIGS 

 WITHIN ONE HOUR 



The following table furnishes an index to the degree of 

 tolerance established in rabbits through the administration 

 of gradually increasing doses of the poison: 



TABLE VIII 



350 MG. OF THIS POISON CAUSED DEATH IN UNTREATED ANIMALS 

 WITHIN ONE HOUR 



Weight Dose of poison in mgs. and when given. 



Rabbit 



No. grams. 12/12 12/19 12/28 1/9 1/14 1/19 1/26 



1850 200 200 400 500 700 1000 



2800 ' 250 

 1950 300 



300 400 500 

 250 400 600 



700 900 

 700 



1400 

 1000 



2100 200 250 400 500 700 1000 1200 



Died 20 min. after 

 last injection. 



Died 30 min. after 

 last injection. 



Died 35 min. after 

 last injection. 



From a study of the above tables it can be seen that in 

 the case of both guinea-pigs and rabbits after the adminis- 

 tration of several doses of gradually increasing strength, 

 a point is reached at which the animal is able to withstand 



