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 niole- 
11 ilar change in the composition of the serum albumin or globulin, 
which is supplied to the cells from the blood or lymph. The fat may 
lie 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 faul 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 frecmently 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 i 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 
(Xeumeister, " Lehibuch," Ann. 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. 
2 O07n.pt. rend. Acad. d. sc, Paris, 1884, tome xcviii. No. 13. 
3 Hofmeister, Ztsclvr . f . physiol . C'hern., Strassburg, 1878, Bd. i. S. 101. 
4 Arch. f. d. ges. Physiol., Bonn, 1883, Bd. xxxii. S. 619. 
5 Ibid., 1887, Bd. xl. S. 21. 
