DIRECT EXAMINATION 65 



though bacteria, yeasts and mold are present in considerable 

 numbers, they are harmless and do not produce toxic effects 

 when introduced into the digestive tract. This statement is 

 wholly without foundation in fact. On the contrary it is known 

 that certain bacteria, yeasts and molds do cause disease and 

 more or less severe intoxications and intestinal disturbances. 

 The objectionable character of mold is universally recognized 



FIG. 19. Mold colonies in gelatin seen under the low power of the microscope 

 (X 80). This mold developed in the gelatin after it was spread on the screen 

 to dry. This gelatin also contained numerous bacteria. Gelatin thus infected is 

 not suitable for bacteriological purposes neither is it suitable for use as food. 



and nearly all animals refuse to eat moldy and mold contaminated 

 food materials. Various ulcerative diseases of the skin and of 

 the digestive tract are caused by mold organisms. While many 

 of the yeasts are entirely harmless and cause very important 

 fermentative changes, some of them are pathogenic to man while 

 others initiate objectionable fermentation changes in the food 

 substances. 



