8 BULLETIN" 319, U. S. DEPARTMENT OF AGRICULTURE. 



THE VARIOUS FORMS OF FERMENTED MILK. 



If it is considered advisable to use cultures of acid-forming bac- 

 teria, the form in which they are taken becomes an important ques- 

 tion. In large cities one usually has a choice of lactic-acid bacteria 

 from several sources. Buttermilk is usually available, although it is 

 not always of good quality. Sometimes kumiss or kefir can be ob- 

 tained, and at the present time milk coagulated with the so-called 

 Metchnikoff bacillus is sold as yogurt or matzoon and under various 

 trade names. 



CULTURES IN TABLET AND CAPSULE FORM. 



In addition to these freshly prepared preparations several tablets 

 or capsules purporting to be pure and active cultures of the Bacillus 

 hulgaricus are now offered for sale. These are for use in fermenting 



lllllllllll 



rojuu 



Pig. 1. — Organisms causing fermentation of milk. 

 a, Bacillus bulgaricus ; b, lactic-acid bacteria. 



milk or are to be taken directly in place of buttermilk or yogurt. 

 Herschell (39) in his little book on the therapeutic uses of soured 

 milks recommends the use of these preparations in preference to 

 fermented milk, but it should be noted that he is very explicit in his 

 statement that great care should be taken to determine the abun- 

 dance and purity of the desired organism. Bacillus hulgaricus seems 

 to be particularly sensitive to desiccation. When preparing the 

 material in tablet form, therefore, a high percentage of the organ- 

 isms is usually killed, whereas foreign organisms commonly retain 

 their viability. Even when prepared with the best of care, such 

 tablets lose their efficiency so quickly that unless such tablets are used 

 within a time limit of efficiency guaranteed by the maker the results 

 may be disappointing. 



It is very easy to test the purity and activity of these dried cultures. 

 Thoroughly pasteurize a small quantity (about half a pint) of milk 

 by holding it, in a bottle plugged with cotton, at or near the boiling 

 point for an hour or more. When this has cooled add two or three 

 of the tablets and keep in a very warm place overnight. It should 



