332 DR ALISON'S OBSERVATIONS ON 



animal matter becomes effete, — why the absorption of matter once deposited in the 

 textures should be a necessary concomitant of animal life, — or why the elements 

 composing these textures should enter into new combinations, and then should 

 require to be expelled from the body. But I am persuaded it will appear, on ex- 

 amining the subject, that the principle formerly stated, of the transient existence 

 of vl till affinities in every portion of matter which becomes endowed with them, is 

 both supported by sufficient evidence, and adequate to the explanation of these 

 phenomena. 



The leading facts on which this conclusion may be rested are the following : — 



1. We know that a continual process of absorption and change of materials 

 is always going on in every living animal texture, and is, in fact, the cause why 

 a continual act of nutrition (the most characteristic of all the functions of animals) 

 is essential, not only during growth, but even in the decline of the body, to the 

 maintenance of its structure and properties. 



2. We know that, simultaneous with this absorption, there is a continual 

 process of excretion going on from every living animal, and that, by these excre- 

 tions, a quantity of all the elements constituting the animal textures is con- 

 tinually thrown off; and farther, it appears to be indicated, although I cannot 

 say fuUy established by Liebig, that the sum of the chemical elements thrown 

 off by the different excretions sufficiently accounts for (the presence of oxygen 

 and water being kept in mind), not merely the part of the blood which is not ap- 

 plied to the nourishment of the textures, but the whole of the blood.* 



3. We know that the excretions, at least that some of them, not only con- 

 tinue but increase, particularly under any increased muscular exertion, and that 

 their nature remains the same, in an animal deprived of aliment, and in a 

 state of rapid emaciation, as in one that is fully supplied with aliment, and per- 

 fectly nourished. " In a starving man, who is in any way compelled to undergo 

 severe and continued exertion," says Liebig, " more urea is excreted than in the 

 most highly fed individual, if at rest. In fevers, and during rapid emaciation, 

 according to Prout, the urine contains more urea than in health."f 



While these facts prove incontestably that a great part of the matter thrown 

 off from every living body must be the product of absorption from the body it- 

 self, let us next consider the information that we have, as to tjie change which 

 is wrought upon the absorbed materials before they are expelled from the body. 



1. The most leading fact in this part of the subject is, that, in the natm'al 

 state, none of the organic compounds which exist in the textures, appear in any of the 



* See Animal Chemistry, p, 136 and 152. This conclusion, however, is not to be regarded as 

 established, various fallacies being connected with it. In fact, it seems to me only certain that the 

 carbon and nitrogen are in the same proportions in the excretions as in the blood. 



\ Animal Chemistry, p. 139. 



