THE PRODUCTION OF ACTIVE IMMUNITY 161 



TABLE XX 



These animals received two and three immunizing doses 

 of the typhoid residue. The protocol number, the weight, 

 the number of immunizing doses, the interval in days between 

 the last treatment and the inoculation, the amount of 

 culture twenty-four hours old, and the result are given: 



Protocol, Weight, No. of residue, Interval, culture, 



No. gm. treatments. mg. days. c.c. Result. 



220 375 2 100 32 Recovery 



221 495 2 100 33 Death 



222 650 3 150 52 Recovery 



223 480 3 150 5 3 Recovery 



224 435 3 150 53 Recovery 



144 605 3 150 74 Recovery 



145 665 3 150 13 4 Recovery 



The minimum fatal dose of the twenty-four-hour cul- 

 ture of the typhoid bacillus employed in this case is 0.5 

 c.c. It will be seen from Table XVIII that a single dose of 

 100 mg. of the residue gives the animal an immunity of 

 six units at the end of twenty-four hours, and that the 

 immunity was less than eight units at that time. On the 

 third day the immunity was found to be diminishing, but 

 on the sixth day the animal bore twice the fatal dose. The 

 animal which received eight units at the end of the first 

 day evidently was close to the borderline, because it did 

 not die until the second day, and the normal time for an 

 untreated guinea-pig to live after receiving the minimum 

 fatal dose is less than twelve hours. Table XIX shows that 

 a single dose of 50 mg. is quite as efficient as one of 100 mg. 

 Table XX indicates that multiple immunizing doses give 

 a higher degree and a more lasting immunity than that 

 secured by a single dose. 



Theoretical Considerations and Conclusions. We wish to 

 offer certain theories that we have reached after making 

 these experiments. In order to save space we will condense 

 our views as follows: 

 11 



