8 SCIENCE AND PRACTICE OF DAIRYING. 



as Nasse, Henle, Van Bueren, Rheinhardt, H. Meyer, &c., who have 

 carried out researches on the origin of the fat globules in milk, Have 

 demonstrated the fact, that, of all the milk constituents, fat alone, in the 

 form of the fatty cell, is recognizable by the aid of the microscope. One 

 of the first who submitted the gland substance to careful microscopic 

 investigation with a view of elaborating a theory of milk production was 

 Will of Erlangen. By means of his investigations, the theory first dis- 

 tinctly expressed by Virchow, regarding the origin of milk, was formulated. 

 According to this theory, the milk-gland must be regarded, morphologically, 

 as a kind of sebaceous gland. The separation of milk in it takes place 

 just in the same way as that of tallow in the many-layered epithelium of 

 the alveoli; it represents, in reality, the pathological occurrence of a 

 fatty degeneration of the epithelium of the glands. Voit, in his work 

 on the formation of fat in the animal body, supported this theory, which 

 rapidly became popular. He regarded milk as a liquid cell substance as 

 the liquefied cell substance of the milk -glands. By the microscopical 

 investigations of Heidenhain, Voit's conclusions were seriously called in 

 question. According to these researches, the epithelial cells of the alveoli 

 of the glands are only present in one layer; the colostrum bodies possess 

 no significance for the morphology of the formation of milk; and the 

 epithelial cells of the secreting gland are not subject to fatty degenera- 

 tion. What takes place is rather that their free ends suffer degeneration, 

 and that a renewal of the cell material takes place at the opposite end. 

 C. Partsch also comes to the conclusion, from microscopical observations, 

 that the formation of fat in the epithelium of the gland does not exhibit 

 the slighteWresemblance to the formation of fat in the sebaceous cell. 

 As Partsch nowhere met with cells exhibiting fatty degeneration in the 

 epithelial layer of the active milk-glands, and always found the fat on 

 the points of the epithelial cells in single large drops, and the increase in 

 the percentage of albumin in the cells accompanied by an increase in the 

 separation of fat, he regarded it as not proven that the fat of milk is an 

 example of retrogressive metamorphosis of the epithelial cell, but rather 

 that it is separated through the special activity of the cell in the true sense 

 of the word. 



Subsequently Heidenhain, as well as Nissen, advanced the opinion that 

 during the period of lactation the nuclei of the gland -cells constantly 

 increase and successively degenerate. They are then extruded from the 

 cells in which they have been formed, and are finally broken up in the 

 cavities of the glandular vesicles. 



This explains at the same time the method in which the nucleo- 

 albumin, discovered by Lubavin and Hammarsten to be a constituent of 

 milk, enters it. 



