4 BULLETIN 148, U. S. DEPARTMENT OF AGRICULTURE. 



Jensen 1 advised the use of a streptococcus in connection with 

 B. hulgaricus as a starter for suppressing undesirable bacterial 

 growths in the cheese, but offered no proof of the efficiency of this 

 combination of cultures. 



Though it is generally believed that it is the lactic acid produced 

 by different bacteria that gives different varieties their value in pre- 

 venting the growth of undesirable forms of germ life, this assump- 

 tion is seriously questioned by some bacteriologists, who think it 

 possible that the formation of lactic acid is incidental and is not the 

 active inhibiting principle. 



White and Avery 2 point out that cultures of B. hulgaricus grow at 

 relatively high temperatures, forming acid as high as 50° C. (122° F.). 

 They also show that relatively high percentages of acid are formed 

 in milk, reaching as high as 3.1 per cent. 



Hastings and Hammer 3 give 4.09 per cent as the maximum amount 

 of acid found in milk. They find that B. hulgaricus is distributed 

 very widely and generally in dairy products of all kinds. Mention 

 is made especially of its presence in the milk and whey at Swiss- 

 cheese factories. 



Heinemann and Hefferan 4 also noted the general distribution of 

 B. hulgaricus, its high growing temperature and its ability to form 

 acid in milk. 



The authors quoted found a very great difference in the maximum 

 amount and the rapidity of acid formation of different cultures. 

 Cultures also lose their ability to form acid to a great extent when 

 carried under laboratory conditions. The growth of Mycoderma on 

 the surface of the whey starter greatly facilitates the growth of the 

 B. hulgaricus culture used. Thoni 5 in some tests with the Myco- 

 derma found that while the whey culture of B. hulgaricus without 

 the Mycoderma showed at the end of 24 hours 7,000,000 and 18,000,000 

 bacteria per cubic centimeter, with the Mycoderma the numbers 

 were 136,000,000 and 200,000,000, respectively, and the increase of 

 acid with the Mycoderma was more than one-half. 



In our own work we have found that B. hulgaricus can form as high 

 as 2 per cent acid in whey, and we found that with the culture iso- 



1 Jensen, Orla. Leber die im Ernmentalerklise stattfindende Milchsiiuregarung. Milch- 

 wirtschaftliches Zentralblatt, vol. 2, no. 9, p. 393-414. Leipzig, Sept., 1906. 



2 White, Benjamin, and Avery, Oswald T. Observations on certain lactic-acid bacteria 

 of the so-called bulgaricus type. Centralblatt fiir Bakteriologie, Parasitenkunde und 

 Infektionskrankheiten, Abteilung 2, vol. 25, no. 5/9, p. 161-178. Jena, Nov. 30, 1909. 



3 Hastings, Edwin George, and Hammer, B. W. The occurrence and distribution of 

 organisms similar to B. hulgaricus of yogurt. Centralblatt fiir Bakteriologie, Para- 

 sitenkunde und Infektionskrankheiten, Abteilung 2, vol. 25, no. 14/18, p. 419—426. Jena, 

 Dec. 22, 1909. 



4 Heinemann, Paul Gustav, and Hefferan, Mary. A study of Bacillus bulgaricus. Jour- 

 nal of Infectious Diseases, vol. 6, no. 3, pp. 304-318. Chicago, June 12, 1909. 



5 Loc. cit. 



