272 BACTERIOLOGY. 



prevent the animal from biting the tube, this should be 

 passed through a perforated piece of wood, or through a 

 cork-borer which is held firmly in the mouth. Any desired 

 amount of liquid can thus be administered without difficulty. 



In experiments with the bacteria of cholera and 

 typhoid fever, it has been the practice to first introduce 

 into the stomach some sodium carbonate solution. This 

 was done in order to neutralize the free hydrochloric acid 

 of the stomach, which otherwise might destroy the bacteria 

 introduced. Again, it was customary to inject opium into 

 the peritoneal cavity, in order to retard or paralyze the 

 peristaltic action of the intestines. The bacteria were thus 

 given every opportunity to develop in the intestinal canal. 



In his classical studies on cholera, Metschnikov showed 

 that the above precautions can be done away with, and 

 better results obtained by feeding milk suspensions of 

 the germs to new-bom rabbits or guinea-pigs. The intes- 

 tines of the new-born animal are free, at least for a short 

 time, from bacteria. The experimental organism, when 

 introduced under these conditions, is enabled to develop 

 unhindered. The intestinal flora of the adult individual 

 may, in some cases, favor the growth of the invading or- 

 ganism whereas, in other cases, it may exert a positive 

 inhibiting action — microbic association. 



Occasionally, it may be desirable to avoid passage of 

 the material through the stomach. . In that case the mater- 

 ial can be injected directly into the intestines, but to do 

 this properly necessitates a laparotomy. Such intra- 

 duodenal injections are very rarely made. 



Observation of Infected Animals. 



The inoculated animal should be placed by itself, in a 

 suitable cage or jar. Obviously, where a number of ani- 

 mals, as guinea-pigs, are injected with the same material, 

 they may be placed in the same cage. They should be 



