516 SEMEN. 



fat-drops are floating. The globules are bubbles or 

 cells, which contain a yellowish oil. 



The analysis of the yolk of egg shows on an aver- 

 age 45 per cent, of water, 30 per cent, of fat, 15 per 

 cent, of protein compounds, and 1 per cent, of inorganic 

 salts. 



The fat, which can be obtained from the yolk by 

 shaking with ether or, after the yolk is boiled hard, 

 partially by means of pressure, is reddish-yellow, 

 colored by a coloring principle as yet comparatively 

 unknown, perhaps identical with hsematoidin (p. 496). 

 It consists of palmitin and olein. 



The protein compound (formerly called vitellin) is a 

 mixture of casein and other protein compounds. 

 Besides these, there are contained in the yolk lecithin 

 (p. 514), cholesterin, and apparently also glycogen. 



The inorganic ingredients are soda, potassium and 

 sodium chlorides, potassium, calcium and magnesium 

 phosphates, and iron oxide. The potassium salts are 

 more abundantly present than the sodium salts, and 

 earthy phosphates are present in much larger quantity 

 than in the white. 



It is very probable, that the eggs of all classes of 

 animals contain the same ingredients. In the yolk of 

 fishes and several amphibious animals are observed 

 under the microscope transparent crystalline plates, 

 which, however, in different spqcies of animals, possess 

 different forms and properties. They appear to be 

 protein compounds, or at least to be very similar to 

 these. 



17. Semen. 



Animal semen, in a pure condition as formed in the 

 testicles, is a whitish, ropy, inodorous liquid of high 

 specific gravity, and neutral or alkaline reaction ; 

 when ejaculated, it is more translucent, more strongly 

 alkaline, and of a peculiar odor, on account of the 

 presence of the secretions of the prostate and Cowper's 

 glands. It consists of a watery liquid, which con- 

 tains, in a state of suspension, as peculiar, morphologi- 



