THE PRINCIPLE OF VITAL AFFINITY. 330 



excretions, although it can only be through the excretions that they disappear 

 from the body, and although the earthy or saline matters absorbed from the tex- 

 tures are there found. The animal compounds existing in the textures must 

 therefore have undergone a great chemical change, in the process by which they 

 are removed from their place in the living body, and finally expelled from it ; and 

 this notwithstanding that they are placed in circumstances exactly similar to 

 those, in which their previous original separation and deposition from the blood 

 in the minute capillaries took place. 



2. The substances into which these animal compounds (with or without ad- 

 ditions derived directly from the primse vise) have resolved themselves almost en- 

 tirely before they are thrown oif in the excretions, must be, the water which is the 

 basis of all, the carbonic acid thrown off by the lungs and skin, the choleic acid 

 thrown off by the hver, and the urea and uric acid thrown off by the kidneys. 

 All these last we know to be formed in the course of the circulation, not in the or- 

 gans by which they are separated from the blood ; and all possess these essential 

 peculiarities, distinguishing them from the compounds forming the textures ; 

 first, that they are crystallizable, i. e., the elements composing them are so ar- 

 ranged as to be capable of assuming the definite forms peculiar to inorganic 

 matter ; and secondly, that they are poisonous to the living body when they are 

 allowed to accumulate in the blood, and, therefore, that their continual expulsion 

 is essential to life. 



3. When we farther examine these compounds, into which the animal tex- 

 tures have resolved themselves before they are expelled from the body, we 

 find that they are substantially the same as those, into which these textures are 

 ultimately converted after death, by help of union with oxygen, when in contact 

 with air and water, and at a certain temperature, — viz., water, carbonic acid, and 

 ammonia, the small quantities of sulphur and phosphorus contained in the ani- 

 mal textures, combining likewise with oxj'gen so as to form sulphuric and phos- 

 phoric acids before they are expelled. 



