104 PKOXIMATE PKINCIPLES OF THE THIRD CLASS. 



or of uric acid. When the urates are thrown down also in the form 

 of a powder, as a urinary deposit, they are usually colored more or 

 less deeply, according to the quantity of urosacine which is preci- 

 pitated with them. 



The organic substances which exist in the body require for their 

 production an abundant supply of similar substances in the food. 

 All highly nutritious articles of diet, therefore, contain more or less 

 of these substances. Still, though nitrogenous matters must be 

 abundantly supplied, under some form, from without, yet the par- 

 ticular kinds of organic substances, characteristic of the tissues, are 

 formed in the body by a transformation of those which are intro- 

 duced with the food. The, organic matters derived from vegetables, 

 though similar in their general characters to those existing in the 

 animal body, are yet specifically different. The gluten of wheat, 

 the legumine of peas and beans, are not the same with animal albu- 

 men and fibrin. The only organic substances taken with animal 

 food, as a general rule, are the albumen of eggs, the casein of milk, 

 and the musculine of flesh; and even these, in the food of the 

 human species, are so altered and coagulated by the process of 

 cooking, as to lose their specific characters before being introduced 

 into the alimentary canal. They are still further changed by the 

 process of digestion, and are absorbed under another form into the 

 blood. But from their subsequent metamorphoses there are formed, 

 in the different parts of the body, osteine, cartilagine, haematine, 

 globuline, and all the other varieties of organic matter that cha- 

 racterize the different tissues. These varieties, therefore, originate 

 as such in the animal economy by the catalytic changes which the 

 ingredients of the blood undergo in nutrition. 



Only a very small quantity of organic matter is discharged 

 with the excretions. The coloring matters of the bile and urine, 

 and the mucus of the urinary bladder, are almost the only ones 

 that find an exit from the body in this way. There is a minute 

 quantity of organic matter exhaled in a volatile form with the 

 breath, and a little also, in all probability, from the cutaneous sur- 

 face. But the entire quantity so discharged bears but a very small 

 proportion to that which is daily introduced with the food. The 

 organic substances, therefore, are decomposed in the interior of the 

 body. They are transformed by the process of destructive assimi- 

 lation, and their elements are finally eliminated and discharged 

 under other forms of combination. 



