166 



Bacteria in Market Milk. 



[Fig. 25. 



genie varieties, to the probably harmless varieties of lactic acid 

 producers. 



The collective group of the Bacterium acidi lactici is the second 

 of importance in the lactic acid group and is also invariably 

 represented in milk. 



While the streptococci produce dextro-rotary lactic acid, among the representatives 

 of Bacterium acidi lactici there are those which produce levo-rotary lactic acid. 

 Since the growth of both species of bacteria depends on the temperature and the method 

 of keeping the milk (in a shallow bowl or in a deep vessel), therefore under certain con- 

 ditions whereby the Bacterium acidi lactici has better chances for vegetating (aerobe, 

 optimum at about 37 deg.), it produces levo-rotary lactic acid and in soiling in deep 

 vessels (the Streptococcus lactis acidi is a facultative anaerobe and grows well at 20 deg.) 

 it produces dextro-rotary lactic acid. These results have been confirmed by the observa- 

 tions of Conn and Esten. The findings of 

 Heinemann, Thiele and Holling that at incuba- 

 tor and room temperature, in milk drawn under 

 specially clean conditions, ' ' d-lactic acid ' ' is 

 formed only at the beginning, are of interest. 



Against the practical utilization of these 

 observations, namely the conclusion that the ex- 

 clusive presence of dextro-rotary lactic acid is 

 dependent on the specially clean procurance of 

 the milk, are the investigations of Pere and 

 Harden, who claim that the nature of the 

 acid formed depends not only on the producer 

 but also in the case of the same producer on 

 the character of experimental procedure; thus 

 for instance one and the same strain of Bac- 

 terium coli produced lactic acid showing opti- 

 cally different properties when cultivated under 

 different conditions, aerobically or anaerobi- 

 cally, etc. 



The Bacillus acidi lactici 

 (Hueppe) group also does not rep- 

 resent constantly uniform species, 

 but it is a collective name which 

 unites all bacteria with especially 



Representatives of the coli-aerogenes Strong acid forming properties that 

 group, from a culture. 1 X 800 (Bac- Ipovi toward <3 tllP Polon and P^TIP- 

 tcrium plilcgmasiac ubcris, after Kitt.) -ledll L clHU 



cially to the aerogenes species. 



The Bacterium acidi lactici Hueppe and the Bacillus pneumonia? Friedlander are 

 similar to the coli-aerogenes species. They are plump, mostly Gram-negative, from cocci 

 to short rods in appearance, forming individually longer rods and short thread-like 

 filaments; they grow luxuriantly, forming moist or almost dry indented colonies with a 

 slimy or jelly-like consistence. In dextrose media usually a strong acid formation 

 takes place. On potatoes the growth is either luxuriant with gas bubbles, or brownish 

 and thin, or transparent. The odor varies, being either disagreeable or pleasant, or at 

 times even odorless. From this description it may be seen that a great number of 

 bacteria are united in this group which are classed by Lohnis as follows: 



1. Type of the Bacillus acidi lactici Hueppe. 



Gas formation with milk coagulation. To these belong the Bacillus aerogenes, 

 Bacillus "a" Guillebean, Bacillus "b" Freudenreich, Bacillus laevolacticus, Bacillus 

 acidi lactici Gortenfeld, also the lactic acid bacilli of Fokker and others which possess 

 differing characteristics, as for instance the formation of esterlike odors, cheesy odors, etc. 



2. Milk coagulation without gas formation. Bacillus Umbatum (acidi lactici) 

 Marpmann, without special tendency to deep growth. Bacillus acidi aromaticus, Bacillus 

 granulosum, crenatum, spirans and ramificans (Weiss) and others. 



3. Gas formation without coagulation of milk, producing white, circumscribed, 

 hemispherical colonies, as for instance the Bacillus pneumoniae Friedlander. 



4. Neither gas formation nor coagulation. 



