454 THE VITREOUS BODY. THE RETINA. [BOOK I. 



The Vitreous Body. 



The vitreous body or humor consists essentially of mucous 

 connective tissue. In the very loose and large meshes of the tissue is 

 contained a large quantity of watery fluid, containing a small 

 quantity of proteids and said to be specially rich in urea (according to 

 Picard containing 0*5 per cent, of that body). 



The following is an analysis of the vitreous body by Lohmeyer 1 . 

 Water in 1000 parts .... 986*400 

 Membranes . . . . . 0*210 



Proteids and mucin (chiefly the latter) 1*360 



Fats 0-016 



Extractive matters (urea, &c.) . . 3*206 



Sodium chloride .... 7757 



Other mineral matters . . . 1*051 



1000000 



The Choroid. 



The middle coat of the eye or Choroid is eminently vascular and 

 contains, imbedded within its substance, branched pigment-cells very 

 similar to those of the frog's skin. Until the researches of Max 

 Schultze had shewn that they properly belonged to the retina, the 

 layer of hexagonal pigment-cells (retinal epithelium) which we shall 

 describe in the sequel were described as an integral part of the 

 choroid. 



All that need now be said in reference to the chemistry of the 

 choroid is that its branched pigment-cells contain a pigment which 

 appears to be similar to, if not absolutely identical with, that which 

 under the term of Fuscin we shall describe as the pigment of the 

 retinal epithelium. 



THE RETINA. 



Introductory. 



The retina is the most internal of the tunics of the eye, and 

 contains the complex terminations of the optic nerve. 



This membrane which by its internal surface lies in contact with, 

 or applied to, the external surface of the vitreous body and which 

 is covered externally by the vascular choroid, possesses during life 

 an exquisite transparency and doubtless throughout its greater part 

 absolute optical homogeneity, so that undulations of light which have 

 traversed the transparent media of the eye and impinge upon the 

 inner surface of the retina, may penetrate to the very peripheral struc- 

 tures which they are destined to throw into action. 



The retina possesses a connective-tissue framework, wherein lie 

 imbedded the greater part of its nervous elements, but which does 



1 Quoted by Gorup-Besanez. 



