THE EYE. 419 



The soluble portion consisted of chloride of sodium, sulphate 

 of lime, and sulphate of magnesia ; the insoluble constituents 

 were phosphate of lime and silica. 



From Van Laer's investigations it appears that the hair con- 

 sists essentially of: 



1. A connecting medium consisting of a tissue yielding ge- 

 latin and represented by the formula C 13 H 10 N 3 O 3 ; and 



2. Of bisulphuret of "protein, C 40 H 31 N 5 O Ia S 9 . 



The large amount of sulphur in hair (averaging 5g) is the 

 cause of its colour being affected by various metallic salts. 

 As there is no constant difference in the results obtained by 

 the analysis of hair of various tints, it is to be presumed that 

 the colour is dependent on peculiar arrangements of the ul- 

 timate particles. 



Hair further contains about 0-4g of peroxide of iron, which 

 is supposed by Van Laer to be chemically combined with the 

 protein.] 



Crystalline Lens and Fluids of the Eye. 



The crystalline lens is insoluble in boiling water, spirit, and 

 acids ; it does not even communicate any turbidity to them ; 

 hence it consists neither of cellular nor elastic tissue, but is a 

 distinct substance, approximating possibly towards horny tissue. 

 The membrana Demoursii, the third layer of the cornea, pos- 

 sesses similar properties, while the true horny layer which lies 

 between the external layer of epithelium and the membrana 

 Demoursii appears to be fibrous, and is converted by boiling 

 into chondrin. The crystalline lens itself possesses a peculiar 

 and very regular fibrous arrangement. Chevenix found the 

 specific gravity of the human lens to be 1079, and that of the 

 sheep 1180. I have observed that the crystalline lens in young 

 animals is softer, and less resisting than at a more advanced 

 age. 



With respect to the chemical composition of the lens, I 

 find that, in addition to albumen, it contains a substance 

 closely resembling casein, to which I apply the term crys- 

 tallin. I reduce the lens to a pulpy mass, stir it with water, 

 and then heat the mixture to the boiling point : the albumen co- 

 agulates, while the crystallin does not coagulate, but is entangled 



