THE KINDS OF MICRO-ORGANISMS IN MILK 



367 



by Hefferan and the writer, and by Gait and lies. Additional 

 proof was brought later by the writer and Ecker and Rahe. 



Rodella classed the so-called acidophil bacteria with the lacto- 

 baciUi, including the Bacillus bifidus of Tissier. Kuntze then 

 showed that there are chiefly two types of bacilli distinguished 

 from each other by their staining properties. While one type, 

 represented by Bacillus bulgaricus, stains solidly with Neisser's 

 stain and alkaline methylene-blue, the other strain shows granules. 

 This latter is the granule bacillus or the "Kornchen" bacillus (Figs. 

 174-176). 



The lactobacilli, as stated before, grow but sparingly on la- 

 boratory media, but growth is favored by the presence of dextrose 

 or lactose. Milk, or a medium pre- r^ 

 pared from milk, such as whey-agar, 

 is the best culture-medium. Rahe, 

 in some studies as to the fermenta- ,, 

 tive power of lactobacilli, used un- 

 neutralized meat-peptone sugar-free 

 broth, with addition of carbohy- 

 drates. Beerwort agar has also been 

 used with some success. By addi- 

 tion of pieces of marble or calcium 

 carbonate in some other form the 

 acid is neutralized as soon as formed, 

 and growth is much prolonged. 



The optimum temperature is usu- 

 ally given as ranging from 40° to 45° 

 C. and even higher, but some strains 

 grow fairly well at lower tempera- 

 ture. At least this must be assumed, 

 since in the ripening of some types of 

 cheese lactobacilli play an important role. This has been shown 

 by Eldredge and Rogers and by Evans, Hastings, and Hart. 



The lactobacilli retain the stain when treated with Gram's 

 iodin solution when the cultures are young, but in old cultures 

 negative forms prevail. If a Gram stain is made of a culture 

 several days old and a red counterstain applied, filaments that are 

 composed of red and blue cells can be frequently observed. The 

 presence of oxygen is not necessary for growth; in fact, anaerobic 

 conditions are preferred by the lactobacilli. 



Owing to the difficulty experienced in attempting cultivation 

 of lactobacilli their wide distribution in nature is a recent discov- 

 ery. Hefferan and the writer found them in the feces of cows, 

 horses, and in human feces; in soil where manure was present; 

 in human saliva; in the gastric juice; in market milk; in various 



Fig. 172. — Colony of Bacillus 

 bulgaricus. 



