EXPERIMENT STATION BULLETINS. 



473 



checked largely by the acid formed. Strain IV grows scantily in 

 skimmed milk, bnt reproduces abundantly when peptone is added; the 

 soluble nitrogenous compounds seem, to be the limiting factor for this 

 strain. This agrees with the results of the Tables VIII, IX, X, where 

 pure cultures of these tv\^o strains in milk were neutralized; Strain II 

 showed an increase in number after neutralization indicating that it 

 was largely the acid which interfered with the growth, while Strain 

 IV did not multiply further even after the acid had been neutralized; 

 lack of available nitrogenous food seems to be a reasonable explana- 

 tion for the behavior of Strain IV. 



The observation of Marshall^ and Marshall and Farrand- that certain 

 bacteria are able to stimulate the acid formation of certain lactic bacteria, 

 can be to some extent accounted for by the preparation of nitrogenous 

 food for the lactic bacteria. Marshall himself has supposed this to be 

 one of the possible explanations. The behavior of the Strains II and 

 IV in mixed cultures make this explanation quite probable. Strain 

 II showed in no case any appreciable increase of acidity in association, 

 while Strain IV gave the following results : 



TABLE XVIII. — Associative Acid Production. 



Cultures. 



Fresh. 



24 hours. 



48 hours. 



96 hours. 



Bad. ladis addi I V alone . . 



Bad. ladis addi IV + B. mycoides . . 

 Bad. ladis addi IV + B. prodigiosns 

 Bad. ladis addi IV + B. subtilis . . . 



B. mycoides alone 



B. prodigiosus alone 



B. iubtilit alone 



21° 



51° 



80° 



95° 



21° 

 21° 

 21° 



66° 

 58° 

 58° 



90° 

 99° 

 81° 



21° 

 21° 

 21° 



26° 

 31° 



22° 



27° 

 35° 

 22° 



93° 

 113° 



92° 



31° 

 36° 

 21° 



The Influence of the Ahsence of ^'ugars. — In this discussion of the in- 

 influence of food upon the fermenting capacity must be included the 

 degeneration of lactic bacteria in sugar-free or sugar-poor media. To see 

 whether such degeneration could be produced by continued transplanting 

 in broth. Strain a was transferred into a tube of meat-peptone broth, 

 from this culture to a second tube and so on. The transfers were made 

 daily. From the first, second, sixth and tenth cultures, milk was inocu- 

 lated and the numbers and acidities of these milk cultures were deter- 

 mined at the beginning and after 24 hours. The result is given in the 

 Table XIX. 



There is a, great variation in the fermenting capacity of the duplicates 

 of the first two transfere which might be accounted for by the influence 

 of the change of medium. After C days' continuous transplantation from 

 broth to broth, the culture became adapted to the medium and the re- 

 sults are homogenous. Since the inoculum was not the same in every 

 case, the first cultures of A and B and the second cultures of C and D 



K'entralbl f. Bakt. II. Bd. 11. p. 739. 

 -Mich. Agrlc. College Special Bui. 42. 



