110 INFECTION AND IMMUNITY. 



injection of diphtheria or tetanus toxins, by which 

 the incubation period can be shortened from sev- 

 eral days down to several hours, depending on the 

 quantity injected. 



The so-called true toxins of bacteria, i. e., those 

 which are able to cause the formation of antitoxins, 

 as a rule are distinguished from other poisonous 

 substances of bacterial or other origin, by the occur- 

 rence of an incubation period when they are admin- 

 istered. However, at least two toxins, venom and 

 that secreted by the Vibrio Nasik and perhaps 

 other vibros, act so quickly that an incubation 

 period is hardly to be recognized. 



Proliferation. The number of micro-organisms originally enter- 

 ing the body is usually quite small; hence the time 

 required for them to reach an infective or toxic 

 quantity probably represents a part of the incuba- 

 tion period. 



In hydrophobia and tetanus a mechanical fac- 

 tor plays a part in the length of this stage. In 

 these cases the micro-organisms (hydrophobia) and 

 toxin (tetanus) appear to reach the central nerv- 

 ous system by way of the peripheral nerves, and 

 symptoms are delayed until this occurs. Wounds 

 of the face and neck are followed by symptoms 

 more quickly than when they are situated on parts 

 more remote from the central nervous system. 

 Adaptation. It is not unlikely that another factor consists of 

 a certain relation between the protective powers of 

 the host and the invasive or aggressive ability of 

 the organism, at least in some instances. Lemaire 

 and also Buxton found that after the injection of 

 pathogenic micro-organisms directly into the cir- 

 culation, there is at first a reduction in their num- 

 ber, followed by renewed proliferation, which 



