228 BOARD OF AGRICULTURE. 



between a plant-eating animal and a flesh-eater, except in 

 the form in which the} 7 consume their food. A hungry plant- 

 eater lives on his own fat and flesh. 



"No single constituent of a plant can support animal life, — 

 neither nitrogenous matter, nor fat, nor sugar, nor mineral 

 substances : it requires a certain definite proportion of each 

 for different classes of animals, and even for different condi- 

 tions of one and the same animal." 



Whilst some of these statements are not original with 

 him, it remains Liebig's great merit to have combined the 

 best thoughts and the best previous observations of others 

 with his own, and thereby give to them a prominence and 

 an influence they never before possessed. Animal physiolo- 

 gists of a more recent date (Voit), without questioning 

 seriously the propriety of Liebig's chemical classification 

 of the constituents of food into plastic and respiratory sub- 

 stances, prefer to arrange them with reference to their quali- 

 fication of preventing a loss of albumen, fat, salines, water, 

 oxygen, &c, in the general transformation of the animal 

 system : they also introduce a third class of substances 

 as important, namely, those which stimulate the activity of 

 the nervous system. As the science of animal physiology, 

 with its devotion to exact modes of investigation into the 

 complicated transformation of the animal system, in spite 

 of its rapid progress, is not yet prepared to exert a control- 

 ling influence on the solution of the practical or economical 

 problem of the fodder question, it is but natural that 

 Liebig's above-stated exposition of the relations of plant- 

 food to animal life, with the exception of the source and the 

 functions of animal fat, is still the generally accepted one 

 in practice. 



Liebig's recognition of the paramount importance of the 

 nitrogenous, the non-nitrogenous, and the mineral con- 

 stituents of plants, regarding their influence on animal life, 

 brought him in opposition to Boussingault and his followers, 

 who, as has been previously stated, ascribed to nitrogen 

 alone a decisive prominence. His assumption, that non- 

 nitrogenous substances, as starch, sugar, &c, assist in the 

 production of fat during the process of digestion, and 

 thereby add directly to the accumulation of fat in the 

 animal system, furnished also a fruitful source of contro- 



