518 URINE. 



brane of the calves' stomach (rennet). When evaporated, 

 a crust of coagulated casein is formed on its surface. 



The colostrum (the secretion of the glands of the 

 breast for the first two or three days after parturition), 

 contains a larger supply of solid ingredients than 

 ordinary milk. In addition to the much smaller milk- 

 globules, larger spherical masses, the so-called granular 

 bodies, which are apparently conglomerations of casein 

 and fat-vesicles, are observed in it. 



Cream, which separates from milk on standing un- 

 disturbed, is formed of the milk-globules, which, being 

 specifically lighter, rise to the surface. Churning 

 breaks up the envelopes of the globules, and their con- 

 tents then adhere together, forming butter. The yellow 

 color of butter is accidental, and arises from certain 

 constituents of the food. In rancid butter, traces of 

 fatty acids have become free. Butter fuses at about 

 32. 



Judging from the products that have been obtained 

 by the saponification of cow's milk, the latter is a 

 mixture of several varieties of fat (compare Glycerin 

 p. 168), which, however, have not as yet allowed of 

 separation. The fatty acids obtained from them are 

 palmitic, stearic, and oleic acids, which form the prin- 

 cipal quantity ; further myristic, butyric, caproic, ca- 

 prylic, and capric acids. Whether the same varieties 

 of fat are contained in the milk of all animals is unin- 

 vestigated. 



19. Urine. 



The urine is secreted by the kidneys from arterial 

 blood. The kidneys consist of microscopical canals 

 (tubuli uriniferi), which are distributed in the cortical 

 substance and towards their open ends unite forming 

 pyramidal tufts, of which each one is grasped at the 

 apex by a short cylindrical sheath, the calyx. The 

 calyces empty into a common larger sac, the pelvis of 

 the kidney. This is continued by the ureter, which in 

 its turn conducts the urine into the bladder. The 

 tubes of the cortical substance commence partially as 



