ANIMAL SUBSTANCES. 139 



Oil Animal oils are fat, tallow, butter, &c. 

 They are mostly solid at the usual temperature. 

 They may be rendered fluid by heat. Oil is ob- 

 tained in great quantities from certain fish, parti- 

 cularly the whale, seal, &c. and fish oil continues 

 fluid. It is very similar to vegetable oil in its other 

 properties. Spermaceti somewhat resembles wax, 

 and is obtained from the head of a species of whale. 

 Animal fibre may be converted into a substance 

 like spermaceti by treatment with the nitric acid, 

 or by exposing it to a current of running water for 

 several months. This has been called adipocire. 

 It has been shown lately that fat is a compound 

 body, consisting of a substance solid and much like 

 wax, which has been called stearin, and a fluid oil 

 called elain. 



Milk is a substance secreted by certain animals 

 for the nourishment of their young. As is well 

 known, milk on standing for a day throws up cream 

 to the surface. Cream has much of the properties 

 of an oil, and when agitated by churning, butter is 

 separated from it. If milk stands until it becomes 

 sour, it separates into a coagulum and a whey. 

 This change may be more completely effected by 

 adding to the milk a small quantity of certain sub- 

 stances, as acids, or rennet, procured by boiling in 

 water the inner coat of the stomach of a calf. 

 The coagulum is thus made more solid, and when 

 pressed and dried it forms cheese. 



In animal bodies there are also found several pe- 

 culiar acids. 



The lactic acid is found in spur whey. It com- 

 bines with the earths and alkalies, forming salts 

 called lactates. It resembles much the acetic acid. 

 The uric acid is found in urine. The substance 

 voided with the urine called gravel, and also those 



