THE PRINCIPLE OF VITAL AFFINITY. 3I7 



" Such a formation of ammonia continually takes place in the soil. There, at- 

 mospheric air is present, and consequently nitrogen ; hydrogen is continually libe- 

 rated, and thus the conditions necessary to the formation of ammonia are ful- 

 filled as often as cellulose, ligneous matter, starch, &c., are changed either into 

 humic acid, or into other constituents of the soil." 



That a partial decomposition of organized matter takes place in the stomach, 

 and is, indeed, the first part of the changes occurring during digestion, seems to 

 be sufficiently proved by some curious and important observations of Liebig 

 himself* " The fresh lining membrane of the stomach of a calf, digested with 

 weak muriatic acid, gives to this fluid no power of dissolving boiled flesh or coa- 

 gulated white of egg" (the supposed property of the Pepsin, or extract of the mu- 

 cous membrane there.) " But if previously allowed to dry, or if left for a time in 

 water, it then yields, to water acidulated with muriatic acid, a substance in mi- 

 nute quantity, the decomposition of which is already commenced, and is com- 

 pleted in the solution. If coagulated albumen be placed in this solution, the 

 state of decomposition is communicated to it, flrst at the edges, which become 

 translucent, pass into a mucilage, and flnally dissolve. The same change gradu- 

 ally affects the whole mass, and, at last, it is entirely dissolved." 



I think we cannot doubt, therefore, that the an- introduced into the stomach 

 of animals, and decomposed there, as Liebig supposes, must be in circumstances 

 peculiarly well adapted for the generation of ammonia, or the setting free of its 

 elements ; which, as we have seen, is all that appears necessary to explain the 

 gradual formation in the matters absorbed from the stomach, of albumen out of 

 non-azotised ingesta ; under the influence of vital affinities, similar to those by 

 which albumen is formed in vegetaljles. 



I am aware that Liebig states with confidence that experiments prove that 

 the whole of the azote excreted in a given time by an animal, is not more than that 

 which is taken in by its albuminous ingesta ; but in this he relies chiefly on the 

 experiments of Boussingault, and these experiments are not considered by the 

 author himself as altogether satisfactory ; nor can they be satisfactory without 

 farther investigation of the quantity excreted by the skin and lungs, into which he 

 did not inquire. (See Dumas, p. 106.) 



I admit it to be certain, however, from a simple comparison of the quantities 

 of albuminous ingesta and the azotised excretions, that the formation of albumen 

 in animals can be to no great extent ; and I am clearly of opinion that the distinc- 

 tion drawn by Liebig, of the azotised and non-azotised ingesta of animals, and the 

 evidence he has given of the chief destination and use of each, constitute the most 

 important improvement lately made, in this department of physiology. It ap- 

 pears now ascertained ; \st. That the latter class of aliments are incapable. In 



* Animal Chemistry, pp. 110-1. 

 VOL. XVX. PART III. 4 L 



