178 BACTERIOLOGY 



CHAPTEE VIII 



IIICBO-OEGANISMS IN ARTICLES OF DIET 



Methods of examining different foods. — As in examining 

 the micro-organisms in water and in the soil, so also articles 

 of diet are tested for the bacteria which they contain by- 

 means of the process of plate-culture. Many such articles 

 are impregnated with bacteria, owing to contamination with 

 adherent particles of earth or germs from the air ; whilst 

 probably insects, particularly flies, play an important part 

 in the transmission of the microbes to them. Many food- 

 stuffs, again, form a very favourable nidus for some of the 

 bacteria — for example, milk, meat, and soup for the bacilli of 

 typhoid fever and cholera — while others, such as the milk and 

 flesh of animals suffering from tubercular disease (Perlsucht), 

 are directly infectious, owing to the bacteria in them. 



In the case of vegetables aqueous infusions are made, 

 from which samples are taken for microscopic examination. 

 Cheese is examined by rubbing up a little of it with water, 

 and using minute particles of the mass to make plate-cultures ; 

 milk is treated like other liquids, and butter and similar 

 substances are submitted to examination either with or 

 without the addition of fluid, according to their consistence. 



When it is not possible to prepare plate-cultures imme- 

 diately, a sample of the substance to be examined is taken 

 with the sterilised platinum wire, and a thrust-culture in 

 gelatine made therewith, from which further investigations 

 can be carried on. Still, this procedure comes far behind 



