556 



THE NERVOUS SYSTEM. 



Water 86 to 89 per cent. 



Solids 14 "11 " 



Proteids (globulin coagulating at 50 per cent., 



albumin, and mucin) 4 6 



Gelatin 13 17 



Cholesterin 0.3 0.8 



Lecithin 1 2.9 



Fat 0.05 0.5 



Salts 0.7 1.2 



Retinal Pigments. The black retinal pigment is fuscin, and is 



Practically identical with the pigment of the iris and choroid. 

 t belongs to the group of pigments called melanins, and differs 

 but little if at all from the coloring-matter in the skin of negroes 

 and in melanotic tumors. Fuscin contains iron, but it is still 

 undecided whether it is derived from hemoglobin or not. 



Rhodopsin or visual purple is the pigment in the outer portion 

 of the retinal rods ; it bleaches out when exposed to light, and is 

 supposed to be derived from fuscin. The chemistry of this pig- 

 ment is undetermined. Of the yellow pigment characteristic of 

 the macula lutea but little is known. 



Aqueous Humor. This fluid is lymph. Its analysis is as 

 follows : 



Water 98.687 per cent. 



Solids 1.313 " 



{Fibrinogen ^ 



Serum-albumin L 0.122 " 

 Serum-globulin J 



Extractives 0.421 " 



Inorganic salts 0.77 " 



Sodium chlorid 0.689 " 



Vitreous Humor. From the hyaloid membrane gelatin may be 

 obtained, also mucoid and a small amount of proteid. 



Crystalline Lens. The following is the analysis of the lens : 



Water ' 63.5 percent. 



Solids 

 Proteids . 

 Lecithin . 

 Cholesterin 

 Fats . . . 

 Salts 



36.5 

 34.93 

 0.23 

 0.22 

 0.29 

 0.82 



The proteid is a globulin called crystallin or, rather, a-crys- 

 tallin and ^-crystallin ; there is also a small amount of albumin 

 in the lens. In the " proteids " is a considerable amount about 

 48 per cent. of an albuminoid substance, insoluble in water and 

 saline solutions. 



Ocular Muscles (Figs. 333, 334). The muscles which move the 

 eyeball are 6 in number : (1) Superior rectus ; (2) inferior rectus ; 

 internal rectus ; (4) external rectus ; (5) superior oblique ; 

 inferior oblique. 



