10 SCIENCE AND PRACTICE OF DAIRYING. 



position of milk at animal heat the percentage of its albumin remains- 

 unaltered, and that its percentage of caseous matter, instead of becoming 

 increased, is rather diminished, while the percentage of peptones present 

 in it increases. Following the researches of Kemmerich, Danhardt 

 endeavoured in 1870 to separate a ferment from the milk-gland of a 

 guinea-pig. In this he succeeded, and with it he was able, by digesting 

 in it a dilute and slightly alkaline solution of egg albumin, to obtain a 

 body having the properties of casein. In 1833, H. Thierf elder published 

 a work which likewise aimed at tracing the formation of the constituents 

 of milk to maternal substances and ferments in the milk-gland and in 

 the milk. Thierfelder believed that his researches pointed to the fact 

 that during the digestion of the milk-gland at animal heat, a body (perhaps 

 milk-sugar) was formed by fermentation processes, which not only pos- 

 sessed the reducing power, but also the properties of casein (perhaps casein 

 itself). The researches of Hoppe-Seyler, Kemmerich, Soubotin, Zahn, 

 Danhardt, and Thierfelder, however, which have been mentioned above, 

 have collectively raised the important objection, that these experiments 

 were not carried out with sufficient care, to exclude the possibility or 

 probability of contamination with micro-organisms, through want of 

 cleanliness in the materials experimented with. 



What takes place in the formation of milk in the udder is, 

 therefore, not as yet well understood. We do not know to what 

 extent the constituents of the blood, the fat, the albuminoids, the 

 carbohydrates, as well as the lymph bodies and the substance form- 

 ing the epithelial cells of the alveoli of the glands, are utilized in 

 the formation of the organic constituents of milk; and still less do 

 we know the changes that take place in the materials which are 

 converted into the constituents of the milk. It may be regarded as- 

 probable that milk-fat is a secretion of the epithelial cells of the 

 gland vesicles of the udder, and that it is derived from different 

 sources, viz., partly from the fat present in the blood, and partly 

 from the products of the changes that take place in the animal 

 tissue. With regard to the albuminoids, the milk-sugar, and the 

 other constituents of milk, despite many researches, little is known. 

 All the most recent scientific investigations, combined with num- 

 berless practical observations of cow-feeders, so far agree that the 

 secretion of milk depends primarily on the direct influence of the 

 greater or less activity, as well as the efficiency, of the milk-gland r 

 and on the particular conditions under which the animal lives; and 

 secondly, on the kind of food and condition of the blood. This 



