38 POISONOUS PKOTEINS 



the rate at which the bacillus multiples. This 

 work was done with a bacillus, 1 c.c. of a twelve 

 hour or older bouillon culture of which invari- 

 ably killed within twenty-four hours. When 

 this amount was given no effects became visible 

 for a period of from ten to twelve hours. With 

 larger doses the period of incubation was some- 

 what shorter, but with the largest doses of the 

 richest cultures there is still a period of incu- 

 bation. This measures the time necessary for 

 two things to happen. First the bacillus must 

 multiply sufficiently to supply enough poison to 

 visibly affect the animal. Second, this poison 

 must be made effective by being split out of the 

 large molecule of which it is a part. Therefore, 

 while the period of incubation is not accompa- 

 nied by the development of symptoms which 

 rise to the plane of observation, it is actually a 

 critical period in every infection and the out- 

 come depends upon whether the bacteria are all 

 destroyed before a lethal dose of the poison has 

 been developed by the multiplication of the ba- 

 cillus and set free or made effective by the se- 

 cretions of the body cells. It is during this 

 period that natural and acquired immunity 

 either save the day or, for the time at least, fail. 

 In natural infection the number of bacilli in- 

 troduced is small and in case of full immunity 



