GENERAL OBSERVATIONS 37! 



can be exalted or attenuated, whilst the size of the dose 

 may be increased or diminished. The third factor 

 also varies, not only amongst different species of 

 animals, but also amongst different individuals of the 

 same species. The essential causes of this variation 

 are not so obvious, so that beyond selecting the animals 

 intended for similar experiments with regard to such 

 points as age, size or sex, but little can be done to 

 standardise cell resistance. 



Immediately an animal has been inoculated a period 

 of clinical observation must be entered upon, which 

 should only terminate with the death of the animal. 

 The general observations should at first and if the 

 infection is an acute one, be made daily later, and if 

 the animal appears to be unaffected or if the infection 

 is chronic, both general and special observations 

 should be carried out at weekly intervals. If the ani- 

 mal appears to be still unaffected, it should be killed 

 with chloroform vapour at the end of two or three 

 months and a complete post-mortem carried out. 



A. The general observations should take cognisance 

 of: 



1. General appearance. The experimental animal 

 should be inspected daily, not only with a view to 

 detecting symptoms due to the experimental infection, 

 but also to prevent any intercurrent infection, natur- 

 ally acquired, from escaping notice (vide page 337). 



2. The weight of the inoculated animal should be 

 observed and recorded each day during the course 

 of an experimental infection at precisely the same hour, 

 preferably just before the morning feed. 



3. The temperature should similarly be recorded 

 daily, if not more frequently, during the whole period 

 the animal is under observation, and carefully charted 

 individual variations will at once become apparent. 

 It should be borne in mind that the temperature re- 

 garded as normal for man (37.5 C.) is not the normal 



