THE EYE. 397 



1.009. Its quantitative composition has already been given (page 

 343). According to Griinhagen, it contains traces of paralactic acid, 

 a dextrorotatory body, and a reducing substance, which is not sugar. 

 Both the latter are unknown. The albumins in question are serum- 

 albumin, serum-globulin, and traces of fibrinogen. 



The Crystalline Lens. The capsule of the crystalline lens, 

 like Descemet's membrane, consists essentially of a membranin, 

 which is not identical with that found in the latter, however, as it 

 is less resistant to the action of boiling water and of acids and alka- 

 lies. According to Morner, it contains 14.10 per cent, of nitrogen 

 and 0.83 per cent, of sulphur. 



A general idea of the chemical composition of the lens itself may 

 be formed from the following analysis, which I have taken from 

 Neumeister : 



Per cent. 



Water 63.50 



Solids 36.50 



Albumins 35.00 



Insoluble albuminoid 17.00 



/3-crystalline 11.00 



rt-crystalline 6.80 



Albumin 0.20 



Fats . 0.29 



Lecithins 0.23 



Cholesterin 0.22 



Salts 0.80 



The albumins of the lens can be divided into two groups, viz., 

 those which are soluble in dilute saline solution, and those which are 

 insoluble. The latter group is represented by a substance which is 

 spoken of as albumoid. It is manifestly a true albumin, as it is 

 entirely dissolved by the gastric juice, and does not yield a reducing 

 substance on boiling with mineral acids. It gives all the common 

 color reactions of the true albumins, and has the same elementary 

 composition. In dilute mineral acids and alkalies it dissolves with 

 ease, and is reprecipitated on neutralization. Unlike the alkaline 

 albuminates, however, its solution in dilute alkalies coagulates at 

 50 C., in the presence of 8 .per cent, of sodium chloride. The sub- 

 stance manifestly constitutes the greater portion of the lens-fibres, 

 as the nitrogen and sulphur values of the two are practically the 

 same, viz., N, 16.62 and S, 0,79 per cent, in the case of the albumoid, 

 as compared with N, 16.61 and S, 0.77 of the fibres. It can be shown, 

 moreover, that after extraction of the soluble constituents of the 

 lens the fibrous framework remains and gives the same reactions 

 as the isolated albumoid. Its amount increases from without 

 inward, in accordance with the increasing age of the fibres. 



Aside from a very small amount of serum-albumin, the remaining 

 soluble albumins of the lens are represented by two vitellins, which 

 are termed a-crystalline and /9-crystalline, respectively. Of these, 

 the a-body is notably found in the outer portion of the lens, 

 while the /3-substance occurs in the inner portion more particularly, 



