164 Bacteria in Market Milk. 



The lactic acid yield, however, corresponds even in the extreme 

 cases only to about 98% of the contained milk sugar, as in the mean- 

 time, depending on the variety of the lactic acid producers, the 

 lactic acid itself is again broken up into simpler acids, acetic acid, 

 valerianic acid, succinic acid, and carbonic acid; alcohol, aldehyde 

 and possibly hydrogen result besides the lactic acid. 



In spontaneously coagulated milk mostly inactive lactic acid 

 is found, or a mixture of inactive and dextro-rotary lactic acid ; but 

 only in exceptional cases is pure dextro-rotary lactic acid found 

 (Gunther and Tierf elder). Kozai mostly found only the dextro- 

 rotary polarizing form. 



The lactic acid bacteria may also be considered as ubiquitous 

 micro-organisms ; they have been found in straw, hay, fodder, dust, 

 feces and in the air. Proliferating in milk they soon adapt them- 

 selves to the nutritive medium which at first is not quite suitable 

 for their propagation, and finally they form standard varieties for 

 which the milk is especially adapted. Through continued growing 

 a weakening of the acid forming qualities may develop, and the 

 coagulation of the milk may not take place in spite of their growth, 

 the bacteria having become "milk tired." Under these conditions 

 they may show other properties, the bacteria rendering the milk 

 slimy instead of sour, which is known to be the case with some of 

 the lactic acid streptococci. 



The specific lactic acid bacteria are aerobes, or facultative 

 anaerobes. 



Lohnis separates the specific lactic acid bacteria into four col- 

 lective groups: 



1. Streptococci. 



2. Plump short rods. 



3. Slender, long, lactic acid bacilli. 



4. Micrococci and staphylococci. 



The most frequent of these are the representatives of the 

 streptococcus group. Arranged into wreath-like, shorter or longer 

 bodies, the individual members are characterized by coccus or oval- 

 shaped bodies. On artificial media they frequently manifest vacuo- 

 lar degenerative forms which change the individual microbes to 

 the size of bacilli. Frequently pure diplococcic forms may be found 

 which at their ends are mostly pointed in a lancet shape. Strepto- 

 cocci grown in milk are composed of individual members mostly 

 in the shape of a figure "8" which lie with their long axis in the 

 direction of the chain proving them to be streptococci that entered 

 the milk after its secretion as compared with the forms from the 

 udder. Some of the representatives form capsules but only under 

 special cultural conditions, as for instance in blood medium, while 

 in other media capsule formation appears to be a constant charac- 

 teristic and occurs especially in old milk cultures. 



Most of the streptococci are Gram-positive. They possess no motility and form no 

 spores. On solid media the colonies usually remain delicate and small; in fluid media 



