i2 4 THE CHEMISTRY OF THE TISSUES AND ORGANS. 
most abundant in the inner denser portions of the lens. It yields 
no nuclein on gastric digestion; the small amount of phosphorus it 
contains is due to inorganic phosphates. The soluble proteids of the 
lens are also not nuclein compounds. About one per cent, of the 
soluble proteid is albumin; the rest is globulin. The globulin is 
precipitated by saturation with magnesium sulphate, but not with 
sodium chloride ; in this it resembles vitellin. The globulin consists 
of two proteids, a-crystallin and /S-crystallin. 
a-Crystallm is completely precipitable by saturation with magnesium 
sulphate or with sodium sulphate at 30° C, by the addition of one and a 
half times its volume of saturated ammonium sulphate solution, by a 
stream of carbonic anhydride, and by very dilute acetic or hydrochloric 
acids. It coagulates at 72° C. It contains : N, 16-68 ; S, 0-56 ; C, 52-83 : 
and H, 6-94 per cent. (a) D = -46°-9. 
(3-Crystallin differs from this in its coagulation temperature (64° C.) 
and specific rotatory power («) D — -43°. It contains 17 - 04 nitrogen and 
T27 sulphur per cent. 
a-Crystallin is more abundant in the outer, /3-crystallin in the inner, 
portions of the lens ; the albumin is equally distributed. The lens 
contains no keratin. The proportion between the four proteids in the 
lens as a whole is as follows : — 
Total Proteids. 
Soluble Troteids. 
In Fresh Lens. 
Albuminoid . 
48 "0 per cent. 
17'0 per cent. 
a-Crystallin . 
19-5 
37 per cent. 
6-8 „ 
/3-Crystallin . 
32-0 ,, 
62 
11-0 
Albumin 
0-5 
1 „ 
0-2 
The Mammary Glands. 
The chemical constituents of the mammary gland have not been 
much studied. The principal proteid constituent of the cells is nucleo- 
proteid, which swells with dilute alkali, and yields, by boiling with 
mineral acid, a reducing substance. That a reducing substance (sugar) 
can be obtained from the gland was first noted by Bert, 1 and confirmed 
by Landwehr, 2 who considered its mother substance to be animal-gum ; 
it is considered by Thierf elder 3 to be the mother-substance of lactose. 
It is possible that the nucleo-proteid just mentioned may be the precursor 
of caseinogen. The lactalbumin of milk is not identical with serum 
albumin, so that its presence in milk cannot be explained by a simple 
transudation from the blood. 
The extractives of the mammary gland contain not unimportant 
quantities of hypoxanthine ; 4 they have not been further investigated. 
1 Gaz. held, de med., Paris, 1879, No. 2 ; Goinpt. rend. Acad. d. sc, Paris, tome xcviii. 
2 Arch. f. d. ges. Physiol., Bonn, Bd. xl. S. 21. Thierfelder had previously (ibid., Bd. 
xxxii. S. 6i9) recognised that the substance is not glycogen. 
3 Loc. cit. 
4 Hammarsten, "Physiol. Chem.," S. 378. 
