CHAPTER VI. 



EXPERIMENTS UPON THE LIVING ANIMAL. 



To carry out the last of Koch's postulates, and so 

 complete the chain of evidence in favour of the 

 causal relation of micro-organisms to disease, and 

 to study the mode of action of a pathogenic bac- 

 terium, it is necessary to introduce into a living 

 animal a pure cultivation of the micro-organism 

 in question. For this purpose various animals 

 are employed such as mice, guinea-pigs, rabbits, 

 pigeons, and fowls. 



Inhalation of Micro-organisms. The 

 animals may be made to inhale an atmosphere 

 impregnated with micro-organisms by means of 

 a spray. In this way Friedlander succeeded in 

 administering the bacteria of pneumonia to 

 mice, and the production of tuberculosis by 

 experimental inhalation has thrown light upon 

 the clinical records of cases reported as instances 

 of the infectiousness of phthisis. 



Administration with Food. A sheep fed 

 upon potatoes which have been the medium for 

 the cultivation of the anthrax bacillus dies in a 



