56 INTRODUCTION. 



Urea is described as colorless, and presenting four-sided 

 prisms, or long, " silky, shining needles." It is without 

 smell and has neither acid nor alkaline reaction. 



Uric add is found mostly in the urine of carnivorous 

 animals or those which feed on flesh, and is also seen in 

 urinary calculi, and gouty concretions. The excrements of 

 birds consist almost entirely of this acid, united with am- 

 monia, constituting the guano of commerce. It is precip- 

 itated at a low temperature, aiid the precipitate is at first 

 grey, then a pale rose color on drying it assumes the form 

 of scales this acid readily dissolves urea. 



Animal matters which are destitute of nitrogen. These 

 consist, 



1. Sugar of milk. 



2. Lactic acid. 



3. Fats. 



Sugar of milk, according to chemistry, composes two- 

 fifths of the solid constituents of human milk. It is ob- 

 tained from the whey by evaporation and crystallization, 

 after removing the casein and fat. 



It is easily soluble in water harder than cane-sugar, 

 and slightly sweet. Its specific gravity is 1. 543. Its crys- 

 tals form four-sided prisms. 



Liebig makes its elements consist of carbon, 12 atoms, 

 hydrogen 24, oxygen 2. 



Lactic acid is found in all the fluids and secretions of the 

 body. It exists in a free state in the milk, sweat, urine, 

 and muscles, and in combination with lime, potash, soda 

 and magnesia holds phospate of lime in solution, and is 

 supposed to predominate when this element is deficient in 

 the bones. It is a strong acid, without smell or -color, co- 

 agulates albumen and casein, and is decomposed by heat. 

 Its salts are soluble in water, and crystallizable. 



Fats are found free in the cellular tissue and medulla 

 of bones, or in combination with other substances, as in the 

 milk, brain, hair, wax of the ear, pus, &c. 



