1 58 FERMENT A TION IN MILK 



the lactic acid organisms decrease {see p. 132). It should be 

 added that at room temperature the type of lactic acid produced 

 turns the plane of polarised light to the right, whereas at blood 

 heat it may turn to the left or be inactive (Kozai). 



Other outside conditions play a primary part in lactic fermen- 

 tation. That this is so, has become increasingly apparent as the 

 knowledge of milk changes has grown. Whilst the exact origin of 

 lactic acid bacilli is not known, many bacteriologists hold that they 

 gain entrance to the milk from the surrounding air of byre or dairy. 

 Others maintain that some species, at any rate, are soil bacteria, and 

 associated with certain geographical localities. Russell states that, 

 under ordinary conditions, the organisms found in the teat of the 

 udder are those which produce lactic fermentation. He quotes 

 Bolley and Hall as finding twelve out of sixteen species in the teat 

 of the udder to be lactic acid producers.^ Veranus Moore has 

 arrived at very similar results.^ Rollin Burr has recently investi- 

 gated this subject with a different result.^ He finds that when 

 milk is drawn from the cow in such a manner as to exclude from 

 it dirt and dust from the air, the stalls, and the cow, such milk 

 may contain none of the organisms capable of producing a normal 

 souring of milk. This also has been our experience. The lactic 

 acid organisms are a secondary contamination of the milk from 

 some external source. None of the species of lactic organisms 

 characteristic of the locality in which Burr worked, could be found 

 in the udder. This is in accordance with the results of others who 

 have had the opportunity of examining the udder or milk ducts for 

 lactic bacilli. Out of 300 examinations made of fore-milks drawn 

 directly from the udder into sterile flasks. Burr found only 2 per 

 cent, contained ordinary lactic acid bacteria, and in these cases 

 the origin was probably outside contamination. Conn found the 

 acid organisms present in 5 cases out of 200 examinations, 

 involving 75 cows. He also maintains that the origin of lactic 

 acid bacteria is in external conditions.^ Further, there is the 

 recognised fact which has been pointed out by Conn and 

 Esten, and frequently met with by ourselves, namely, that lactic 

 acid organisms are not the predominant species in freshly drawn 



1 Outlines of Dairy Bacteriology, H. L. Russell, 1898, p. 43. 



2 Twelfth and Thirteenth Reports of the Bureau of Animal Industry, 

 U.S.A., 1895 and 1896, p. 265. 



3 Storr's Agricultural Expt. Sta. Rep. for 1900, pp. 66-81. Centralb.f. Bakt. 

 ii. Abth., 1902, p. 236. 



* Storr's Agricultural Expt. Sta. Rep., 1899, p. 23. 



