124 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-Crystallin 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, O56 ; C, 52*83 ; 

 and H, 6'94 per cent. () D = -46-9. 



|3 Crystallin differs from this in its coagulation temperature (64 C.) 

 and specific rotatory power (a) D =-43. It contains 17 '04 nitrogen and 

 1'27 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 : 



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. hebd. de med., Paris, 1879, No. 2 ; Compt. rend. Acad. d. sc., Paris, tome xcviii. 



2 Arch. f. d. ges. PhysioL, Bonn, Bd. xl. S. 21. Tbierfelder had previously (ibid., Bd. 

 xxxii. S. 6i9) recognised that the substance is not glycogen. 



3 Loc. cit. 



4 Hanimarsten, "PhysioL Chem.," S. 378. 



