BUTYRIC FERMENTATION 159 



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. 



Some authorities have suggested that breed of cow and fodder 

 affect the lactic acid bacteria, and that on this account the milk of 

 certain farms contains more acid organisms than other farms. 

 The probability is that the difference is due to other causes ; but 

 the subject has not been fully worked out. 



TJie function of lactic acid bacteria. — Of all the fermentations 

 occurring in milk and its products, that of lactic acid has by far the 

 highest degree of utility. Many of the other fermentations bring 

 about anomalous conditions in the milk, which are looked upon as 

 "diseases." But the souring of milk and the ripening of cream, 

 both of which are due to lactic acid organisms, may be turned to 

 good account. Of this we shall speak in a later chapter. 



2. Butyric Acid Fermentation 



Lafar states that the first mention of the fact that butyric acid, 

 discovered in 18 14, can also be produced by fermentation, was 

 made by R. Marchand in 1840, in connection with his researches 

 on the composition of the milk of the South American cow-tree 

 {Galactodendron aviericanuvi). In 1841 Noellner described, under 

 the name of pseudo-acetic acid, a substance which he had found 

 to result from the spontaneous decomposition (fermentation) of 

 calcium tartrate, and which was then recognised by Berzelius as 

 a mixture of butyric and acetic acids. Two years later Th. Pelouze 

 and A. Gelis observed that the lactic fermentations instituted by 

 them did not progress satisfactorily, butyric acid and considerable 

 quantities of hydrogen being produced. 



But the discovery of the true state of the case was made in 1861 

 by Pasteur, who showed that two successive processes are here 

 involved : first, the conversion of sugar into lactic acid as calcium 

 lactate, and afterwards the transformation of the lactate into 

 butyrate. He demonstrated that each of these changes is due to 

 a special ferment : in the first place the lactic ferment, in the second 

 place the butyric ferment. But that was not all Indeed, it was 

 by no means the most important attribute of this newly discovered 



