MILK. 517 



cal elements, the spermatic filaments (spermatozoa), 

 microscopic, fibrous bodies, distinguished by the power 

 of motion; and the seminal cells (seminal granules), 

 cells very similar to the colorless blood-corpuscles. 



Semen contains 10-12 per cent, of solid ingredients, 

 which consist of fat, inorganic salts, particularly cal 

 cium phosphate, and a peculiar but slightly known 

 body, spermatin, very similar to mucin (p. 512). The 

 latter is the cause of the gelatinous consistence of 

 semen. Il is not precipitated from its solution by 

 boiling ; by evaporation, however, it is converted 

 into a modification, which is completely insoluble in 

 water. 



18. Milk. 



The characterizing ingredients of milk are fat, casein, 

 (p. 487), and sugar of milk (p. 200). The two latter 

 are present in a state of solution ; the fat is suspended 

 in the form of globules. Besides these, milk contains 

 the ordinary undetermined substances and the salts of 

 the animal fluids (particularly alkaline and earthy 

 phosphates), and also some iron oxide. 



Milk appears under the microscope as a clear liquid, 

 filled with numberless clear globules of different sizes, 

 mostly however smaller than the blood-corpuscles. 

 They are surrounded by an envelope, which incloses 

 the fat. Hence ether, shaken with milk, takes up 

 hardly any fat. This takes place only when the milk 

 has been treated with alkali or acetic acid, and the 

 envelopes broken up by this means. 



The quantity of solid ingredients in milk is vary 

 ing in different animals, and different individuals. 

 &quot;Woman s milk contains 11-13; cow s and goat s milk, 

 13-14 ; mare s milk, 16 ; bitch s milk, 25 per cent. The 

 amount of single ingredients contained in it is just as 

 varying. Fat 3-5, casein 2-8, sugar of milk 2-9, salts 

 0.25-1.5 per cent. 



Milk is, as a rule, slightly alkaline. It does not 

 coagulate by heating, but easily by acids, by voluntary 

 acidification, and in the presence of the mucous mem- 

 44 



