198 A MANUAL OF BACTERIOLOGY 



the toxin. Thus, if an alligator be injected with tetanus 

 toxin, no effect is produced, but the toxin rapidly disappears 

 from the blood. If the animal be kept at ordinary tem- 

 perature (20 C.), although the toxin disappears, antitoxin 

 is not formed, but if it is kept at 30-37 C. antitoxin is 

 rapidly produced. The two experiments together suggest 

 that the toxin is fixed by the cells, but has no effect upon 

 them ; if the. toxin were not fixed, it would be possible to 

 detect it, and presumably it would not produce antitoxin. 

 2. Natural immunity against micro-organisms. A number 

 of factors are doubtless concerned in preserving the body 

 from invasion by micro-organisms, and while non-specific 

 reactions may suffice when the number of organisms is 

 small, specific reactions have to be evoked if the number 

 of organisms is large. The unbroken surfaces of the 

 body have a considerable protective action in preventing 

 the entrance of micro-organisms. The flushing-out action 

 of accelerated circulation will exert some action in elimina- 

 ting organisms from a localised 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 tempera- 

 ture 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 experi- 

 ments 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 chicken 

 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 



