54 



BACTERIOLOGICAL METHODS 



sour milk, ripened cream, ripened cheese, sauerkraut, pickles, 

 etc., the processes of clarification are not applicable, and hence we 

 always find a large number of certain predominating types or 

 species of organisms present. 



The microscopical examination of products which have under- 

 gone normal fermentation shows that the number of organisms 

 present is quite variable, depending upon a variety of causes and 

 conditions. This can readily be ascertained from the examination 



<b o 



oM 



FIG. 14. Substances frequently found in tomato catsup, a, Heat dextrinized 

 corn starch. Starch is frequently used as a filler or stiffening agent, b, bacteria 

 which frequently appear in great numbers, c, Vinegar eels derived from cider or 

 wine vinegar. Soil nematodes may also be found, indicating gross soil contamina- 

 tion and inadequate washing at the cannery, d, Nematode larvae derived from the 

 soil, e, f, g, h, Spore types frequently met with in catsups, i, Yeast cells. 



of such common household products as vinegar, sour cream, cider, 

 apple butter, sour milk, etc. It would be most desirable to de- 

 termine the exact identity of the organisms which produce the 

 most favorable fermentation changes in fermented food products. 

 This has been done in some cases and pure cultures of the specific 

 organisms are used for manufacturing purposes, resulting in the 

 production of superior food articles. When the fermentation 



