EXAMINATION OF POISONOUS FOODS. 229 



In the examination of liquid and semi-liquid foods, such as milk, 

 custard, cream, broths, and jellies, small bits or a few drops should 

 be placed in sterilized media and grown under the conditions above 

 mentioned. 



A growth having occurred in one or more of these tubes, the bac- 

 teria should be examined in hanging-drops and in stained mounts. 

 If more than one organism be present, plate cultures should be made 

 and each germ should again be grown under the conditions men- 

 tioned. 



The infectious character of each organism should be tested on the 

 lower animals : (1) By feeding; (2) by subcutaneous inoculation; 

 (3) by intra-peritoneal inoculation, and (4) by intravenous injection. 

 The animals generally employed in these experiments are white mice, 

 white rats, guinea-pigs, kittens, puppies, and rabbits. A given germ 

 may be toxicogenic to one of these animals and not to the others. 

 The quantity of the bouillon culture — twenty-four hours old or older 

 — employed should be relatively large — from one to ten c.c, accord- 

 ing to the animal and the method of inoculation. If these amounts 

 prove active, smaller quantities should be tried until the limit is 

 reached. 



Cultures sterilized both by filtration and by heat should be tested 

 on animals. It should be borne in mind that certain toxins, notably 

 those of the colon bacilli, are removed from cultures by filtration 

 through porcelain, while they are not altered by a degree of heat 

 sufficient to kill the bacteria. 



If by the above mentioned experiments a toxicogenic germ has been 

 discovered, its morphological, cultural, tinctorial and pathogenic 

 properties may be studied as thoroughly as the investigator may desire. 

 The study of the bacterial poison may also be carried to the same 

 extent. The examination for ptomains and toxins can be carried out 

 according to the methods described in subsequent chapters. 



