TOLERANCE TO ORGANISMS 245 



ised focus of infection just as it does with toxins. The 

 body temperature may be of some importance, and the 

 febrile condition so generally induced by infection is 

 probably to some extent protective and curative. Thus 

 frogs, fish, and chickens are naturally immune to anthrax. 

 In the one case the body temperature is low, 18 C. or 

 thereabouts ; in the other it is high, 40 to 41 C., and 

 this may influence the growth of the anthrax bacillus, 

 preventing the full and rapid development which may be 

 necessary for the production of the disease. That such 

 is the case would seem to be shown by experiments in 

 which when the temperature of the medium is raised or 

 lowered infection takes place ; frogs and fish kept in 

 water raised to a temperature of 35 C., and chickens 

 refrigerated so as to reduce their temperature, all perish 

 from anthrax after inoculation. It is clear, however, that 

 this is not necessarily the only factor, for sparrows, which 

 have a temperature as high as that of the chicken, can 

 be infected with anthrax without refrigerating. Behring 

 'would ascribe the immunity of white rats to anthrax to 

 the high alkalinity of their blood, and claims to have 

 shown experimentally that a vegetable diet reduces this, 

 and fatigue is said to act similarly. 



In some cases the animal, after invasion by the organism, 

 becomes gradually tolerant to its presence (immunitas 

 non sterilisans). This is particularly the case in proto- 

 zoan infections, e.g. piroplasmosis. The animal, after a 

 period of ill health, gradually recovers, though the 

 organisms may still be present, as can be demonstrated 

 by injecting some of its blood into a susceptible animal. 

 Conceivably the receptors necessary for the intoxication 

 become gradually used up, and when this state is attained 

 the animal becomes insusceptible. 



The blood, lymph, and other fluids and tissue juices 

 sometimes exert a more or less germicidal action on 



