FORMATION OF THE ORGANIC CONSTITUENTS. 665 



at in this light, certain substances may be said to stimulate the cells of the glands 

 to increased activity in all directions, tending to the production of a larger 

 quantity of milk rich in all kinds of solid constituents ; whilst other substances 

 may be looked upon as stimulating the cells in a special manner, tending 

 to the increased production of certain only of the constituents of the milk. 



Place of formation of the organic constituents. As already 

 noticed, the fact that the chief organic constituents of the milk are 

 peculiar to the secretion, and do not occur as such in the blood or 

 lymph, may be regarded as sufficient evidence of their being formed in 

 the gland itself. 1 The casein is in all probability produced by a mole- 

 cular change in the composition of the serum albumin or globulin, 

 which is supplied to the cells from the blood or lymph. The fat may 

 be formed by the cells of the gland from proteid, or possibly even from 

 carbohydrate materials furnished by the blood ; or it may be taken up 

 directly from fat which has been formed elsewhere, and which is always 

 present in a certain small amount in blood and lymph. For while, on 

 the one hand, there exists no clear evidence to show that the mammary 

 gland can itself manufacture fat, it is extremely probable that, in 

 common with most if not all other cells in the body, the cells of this 

 gland do possess such a faculty. With regard to the characteristic 

 sugar of the secretion, and which, being characteristic, must be pro- 

 duced by the gland itself, there is some evidence to show that this is 

 formed from dextrose, which is itself manufactured elsewhere than in 

 the gland. That this is so would appear from the following experiment 

 by Paul Bert. 2 Bert removed the mammary glands from goats, 

 then allowed them to become pregnant. After parturition, the 

 urine, during three days, contained a substance which reduced cupric 

 oxide and appeared to be dextrose. This was not present before par- 

 turition, nor was it found in normal animals either before or after 

 parturition; it was therefore presumably formed in the organism in 

 larger amount than usual for the purpose of becoming converted into 

 lactose in the mammary gland. 



In view of the fact that lactose is frequently found in the urine in women, 

 and in mammals generally, immediately before and after parturition, 3 this 

 experiment of Bert seems to need repetition, especially since he appears not to 

 have isolated or carefully examined the reducing substance which he detected. 

 The lactose found in the urine after parturition has generally been supposed 

 to be re-absorbed from the secretion which has formed in the alveoli and ducts 

 of the mammary glands. 



Thierf elder 4 has pointed out that both the casein and sugar of milk could 

 be derived from the nucleo-proteids or glyco-proteids of the gland-cells by a 

 process of splitting. In support of this view, a formation of lactose is said to 

 occur on keeping portions of minced fresh mammary gland in normal saline 

 solution at the temperature of the body ; the lactose being preceded by a colloid 

 carbohydrate, identical, according to Landwehr, 5 with his " animal gum." This, 

 however, does not affect the question of the ultimate sources of origin of these 



1 A small quantity of casein is said to occur in the secretion of the sebaceous glands 

 (Neumeister, "Lehrbuch," Aufl. ii. S. 496). This is of interest in connection with 

 the fact that the mammary glands have been regarded as representing enlarged and 

 modified sebaceous glands. 



" Compt. rend. Acad. d, sc., Paris, 1884, tome xcviii. No. 13. 



3 Hofmeister, Ztschr.f.pkysioL Chem., Strassburg, 1878, Bd. i. S. 101. 



4 Arch.f. d. ges. PAy*wtf., Bonn, 1883, Bd. xxxii. S. 619. 



5 Ibid., 1887, Bd. xl. S. 21. 



