CHAPTER XVIII. 



THE EYE AND THE EAR. 



THE EYE. 



IN studying the chemical composition of the eye, we shall con- 

 sider the most important parts of the organ in succession. It 

 should be pointed out in advance, however, that the subject has 

 thus far received but little attention, and our account must hence of 

 necessity be very imperfect. 



The Cornea. An analysis of the cornea of the ox has given 

 the following results: 



Pro mille. 



Water 758.3 



Solids 241.7 



Collagen 203.8 



Other organic substances 28.4 



Mineral salts 9.2 



The collagen, which forms the greater portion of the fibrous net- 

 work of the cornea, is probably identical with the common form 

 which can be isolated from cartilage, and, according to Morner, con- 

 tains 16.95 per cent, of nitrogen. 



The semiliquid inter fibrillary substance consists of a mucoid, 

 which yields a reducing substance on boiling with dilute mineral 

 acids. It contains about 2 per cent, of sulphur, and seems to be 

 characteristic of corneal tissue. In addition, we find two globulins, 

 which, according to Morner, do not belong to the cornea proper, 

 however, but are contained in the epithelial layer. Nucleins have 

 not been found. 



Descemet's membrane principally consists of a membranin, which 

 contains 14.77 per cent, of nitrogen, and 0.90 per cent, of sulphur. 

 The substance is a glucoproteid, and belongs to the group of hyalo- 

 gens (which see). On boiling with dilute hydrochloric acid it yields 

 a reducing substance. In ordinary boiling water it is insoluble, but 

 dissolves under the action of superheated steam. It is digested 

 by trypsin, while the gastric juice is without effect. 



The Sclerotic. The composition of the sclerotic coat of the 

 eye is very much the same as that of the cornea, but it appears that 

 the quantity of the mucoid is here much less, while collagen repre- 

 sents about seven-eighths of the entire amount of solids. 



The Aqueous Humor. The aqueous humor is a clear fluid of 

 an alkaline reaction and a specific gravity varying between 1.003 and 



396 



