LACTIC ACID FERMENTATION 197 



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 mi\k. This also has been the 

 experience of the writer. 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 Swithinbank and the writer, namely, 

 that lactic acid organisms are not the predominant species in freshly- 

 drawn milk, as they undoubtedly would be were they organisms 

 of the udder. Hence there can, we think, be little doubt that the 

 origin of lactic acid organisms is to be found in some external 

 condition or conditions. 



It follows from what has been said that cleanliness of byre, dairy, 

 and general manipulation is an important factor in the presence, 

 both actual and in degree, of lactic acid organisms. 



(2) Butyric Acid Fermentation. — This form of fermentation is 

 also one which we have previously considered. Both in lactic and 

 butyric fermentation we must recognise that in the decomposition of 

 milk-sugar there are almost always a number of minor products 

 occurring. Some of the chief of these are gases. Hydrogen, carbonic 

 acid, nitrogen, and methane occur, and cause a characteristic effect 

 which is frequently deleterious to the flavour of the ijiilk and its 

 products. Most of the gas-producing ferments are members of the 

 lactic acid group, and are sometimes classified in a group by them- 

 selves. In butyric fermentation of milk the three chief products 

 are butyric acid (which causes the bitterness), hydrogen, and carbonic 

 acid gas. 



(3) Coagulation Fermentations without Acid Production. — Of these 

 there are several, caused by different bacteria. What happens is 

 that the milk coagulates, but no acid is produced, the whey being 

 sweet to the taste rather than otherwise. The condition is in the 



* Store's Agricultural Expt. Sta. Rep. for 1900, pp. 66-81. Centralh. f. Bakt., 

 Abth. ii., 1902, p. 236. 



f Storr's Agricultural Expt. Sta. JRep., 1899, p. 23, 



