THE BACILLUS FOR SMALL ANIMALS 171 



In rabbits the temperature is never high, and the 

 absence of other signs of intoxication is a marked 

 feature. The natural immunity of these animals to 

 Johne's bacillus is not sufficient to safeguard them 

 against a fatal termination of the experiment, and we 

 have seen that the saprophytic B. phlei may cause 

 rapid death of the animal, although the latter is en- 

 dowed with an immunity against this bacillus. This 

 may be appreciated more easily by a brief considera- 

 tion of what takes place in animals inoculated with 

 B. phlei. Although B. phlei is a saprophytic micro- 

 organism, when inoculated intravenously into rabbits 

 it causes a rise of temperature within the first twenty- 

 four hours. This is presumably due to a toxin secreted 

 by the bacillus, the animal possibly producing anti- 

 bodies to the toxin, which may neutralize it completely 

 by the fourth or fifth day after the injection, at which 

 time, as we have seen, the temperature falls more 

 or less to the normal. 



An intraperitoneal or subcutaneous inoculation pro- 

 duces no rise of temperature. In these cases it is 

 probable that the toxin is absorbed by the liver or 

 subcutaneous tissue, and thus does not reach the heat- 

 regulating centres of the brain. That the crisis is not 

 caused by the death of the bacilli inside the animal 

 body, or by the excretion of the bacilli, is proved by 

 following closely the condition of the kidneys. It is 

 true that cultures may be obtained from the urine 

 twenty-four hours after inoculation, but on micro- 

 scopical examination of the organs the number of 

 bacilli present is very small, and in some cases they 

 cannot be found even after a prolonged examina- 

 tion. 



On the other hand, it is not until the third or fourth 

 day that the kidney becomes invaded by a large number 



