CHEMICAL COMPOSITION OF THE BODY. 



91 



sembling gum anibic when dried, soluble in water, less in alcohol, and still 

 less in ether. It gives a precipitate with many metallic salts. It forms the 

 chief mass of the so-called Extractive of the urine, and its reactions ex- 

 plain the statements that have been made in regard to the presence of sugar 

 in the urine. It is quadribasic, and has a composition represented by the 

 formula C 10 H 18 N,O I0 . 



ALLANTOIN, C 4 H,.N 4 O 3 . As its name implies, this substance is found in 

 the allantoic fluid of the cow, but it also appears in the acid urine of foetal 



FIG. 50. 



FIG. 51. 



Allantoin. 



Cystin. 



and sucking animals that is, during the period of life when the herbivora 

 are subsisting on animal food. It has also been found in human urine after 

 the free use of tannic acid. It forms transparent prismatic crystals, soluble 

 with difficulty in cold, but more easily in hot water and in boiling alcohol. 

 It is insoluble in ether. It is closely allied to uric acid and to urea in fact, 

 under the influence of yeast it breaks up into urea and salts of ammonia 

 and is consequently one of the terminal products of the disintegration of 

 albumen. It is not precipitated by corrosive sublimate nor by the salts of 

 lead. It has been found in the urine of dogs suffering from diseases of the 

 lungs, apparently in consequence of the deficient supply of oxygen imped- 

 ing the formation of the uric acid ordinarily present. 



CYSTIN, C 3 H 6 NO 4 iS.,. A rare constituent of the urine of apparently 

 healthy persons, and of renal and vesical calculi. It is normally present in 

 the kidneys of oxen. It forms transparent, colorless, six-sided plates or 

 tables, insoluble in water and alcohol, but soluble in mineral acids, in oxalic 

 acid, and in caustic and carbonated alkalies. It is, however, precipitated 

 by ammonium carbonate from its acid, and by acetic acid from its alkaline 

 solutions. Like the foregoing substances, it is in all probability a transition 

 stage of the decomposition of albumen or other nearly allied sulphur-hold- 

 ing compound. Its rarity shows that it is the result of a morbid process. 



UREA, C. 2 H 4 N 2 2 , crystallizes in white silky, four-sided prisms, which 

 frequently present oblique or dihedral summits. It possesses a bitter cool- 

 ing taste, like saltpetre, is deliquescent, and very soluble in water and alco- 

 hol, but somewhat less so in ether. It has no action on vegetable colors. 

 It is decomposed at 212 F., giving off ammonia. It is not affected by 

 potassium permanganate or ozone, but by nitric acid it is decomposed into 

 water, nitrogen, and carbonic acid. Strong mineral acids, and the hydrates 

 of the alkalies, as well as contact with albuminous compounds undergoing 

 putrefaction, effect its conversion into ammonium carbonate. It unites with 

 nitric and oxalic acids to form salts. It is isomeric with ammonium cyanate, 

 contains 46 per cent, of nitrogen, and is one of the terminal products of the 



