FORMATION OF MILK. 9 



Bizzozero and Vassate, by their elaborate investigations on the increase 

 of the constituents of the growing glands of the mammals, and on their 

 capacity for undergoing regeneration when fully developed, came to the 

 conclusion that in milk we have not to deal with a secretion of the gland- 

 cells. At the same time they established the fact that no evidence exists 

 of a direct or indirect division of the epithelium of the glands during 

 lactation, and hence that the process of milk formation is independent 

 of the destruction of cells or of cell nuclei, as Heidenhain and Nissen had 

 affirmed. 



Rauber regards milk-fat as a decomposition product of the lymph 

 bodies of the blood, which, as he believes, can be proved to float in the 

 gland alveoli, and expresses the opinion that the source of the caseous 

 matter is also to be sought for in the lymph bodies. According to him, 

 a single principle runs through the whole scheme of nourishment of the 

 young mammal, in so far as the lymph bodies already play an imp'ortant 

 part in the nourishment of the egg and of the embryo. With the birth 

 of the young mammal, exit for the lymph bodies on the uterus is closed 

 and a new exit is opened in the milk-glands, so that one and the same 

 material is used for the nourishment of the egg and the embryo as for 

 the nourishment of the young mammal. Through the above-mentioned 

 researches of Heidenhain, Parstch, Bizzozero, and Vassate, the basis of 

 Rauber's conclusions has been for the most part destroyed. 



According to another series of investigations on milk formation, the 

 origin of the different organic constituents of milk in the milk-gland is to 

 be traced to certain maternal substances, and is carried out by certain 

 ferments. Hoppe-Seyler, at the end of 1850, made the observation that 

 if milk be allowed to stand exposed to the air, small quantities of fat, 

 probably from protein matter, were formed. This formation of fat is 

 accompanied by the absorption of oxygen and the evolution of carbonic acid 

 gas. This observation has been confirmed by Kemmerich and Soubotin. 

 It is a matter of dispute, however, whether this process, if it does take 

 place, is to be regarded as a physiological one, or whether it is to be 

 accounted for by the action of bacteria. To decide this point, Kemmerich 

 in 1867 first introduced a method of research which consists in observing 

 the behaviour of the secretion from the milk-gland at the temperature of 

 the body. Supported by the results of a number of experiments, Kemme- 

 rich believed he had established the fact that during the secretion of 

 the milk at animal heat a physiological process goes on, in which caseous 

 matter is formed at the expense of a fermentative decomposition of 

 albumin. This theory of Kemmerich, which in the main was also 

 adopted by Zahn, was totally disproved in the year 1882. Schmidt- 

 Muhlheim, by means of careful researches, proved that during the decom- 



