158 Bacteria in Market Milk. 



Subtilis varieties, mycoid varieties, vinegar bacteria, yeasts, 

 Penicillium glaucum, mucor varieties and aspergilli also grow from 

 to 8 deg. C., as do soil bacteria, fluorescence varieties and bacilli 

 which split up proteids (bitter taste of milk). According to 

 Kniisel, psychrophile bacteria may be demonstrated in sterilized 

 milk, while Bischoff found them in the market milk of Leipsic. 



Bischoff found that in milk which had been cooled to about deg. C., the bacterial 

 number gradually diminished from the third to the seventh day; it then multiplied 

 rapidly, without showing a considerable increase in the degree of acidity. A bacterial 

 rennet formed, however, and the milk coagulated on boiling. This appeared as early as 

 the fourth to seventh day, when the milk was kept between 6 and 8 deg. C. Frozen 

 milk on the other hand keeps for a remarkably long time. 



Kniisel found peptonizing bacteria in sterilized market milk which had been kept 

 at 8 deg. C. ; as a result of their growth the milk had the appearance of soapy water, 

 and possessed a bitter taste. 



Therefore, all milk cannot be protected from spoiling by being 

 kept cool. The milk must be procured at the start with as small a 

 number of bacteria as possible. 



The opposite of these psychrophile species are the thermo- 

 philes, which may be actually isolated from the army of accom- 

 panying bacteria by a high degree of heat. They continue to grow 

 even in temperatures of 70 deg. C., and over (Zettnow), a tem- 

 perature at which most of the vegetative bacteria and to some 

 extent also spores of the mesophiles and psychrophiles are de- 

 stroyed. Such bacteria were found not only in hot springs by 

 Cert'es, Garrigon, Karlinski, Teich, Tsiklinsky, but also in river 

 water (Miquel, Tieghem, F. Colin, MacFadyan and Blaxall, 

 Michaelis and others) ; finally they were found almost everywhere 

 by Globig, and in the intestinal content of animals, feces, manure, 

 liquid manure, in the soil and upon fodder by Rabinowitsch. 



The thermophile species are not directly pathogenic. This 

 group, however, contains several toxin producers, and peptonizers 

 of milk. 



Sporulating bacteria which form spores that resist a heat of 

 100 deg. C. and over should not be confused with the thermophiles. 

 (Peptonizing species, as mycoides, anthracoides, subtilis, mesen- 

 tericus and the butyric acid bacilli). Between the psychrophiles 

 and the thermophile bacteria lie the large army of mesophiles, to 

 which belong most of the ordinary species of bacteria found in 

 market milk. 



Corresponding to their requirements for oxygen they are 

 divided into obligatory aerobes, which propagate only in the 

 presence of oxygen, facultative anaerobes, which can vegetate 

 without oxygen, and obligatory anaerobes, which can grow only in 

 the absence of oxygen. 



They may also be divided, according to the substances which 

 they attack, into those which split sugar, proteids and fats, or, 

 according to the products which they form during their growth in 

 certain media, into acid producers (lactic acid producers, butyric 

 acid producers, etc.), or into alkaligenic species and gas producers, 



