96 BOARD OF AGRICULTURE. 



organism ; the forms and constructions of the principal 

 organs, the history of their deveh)pment and of their growth ; 

 the process of absorption and of secretion, etc. , with a skill and 

 a perseverance which deservedly called forth the admiration 

 of the time ; yet the character of many of the chemical pro- 

 cesses which transpire in the living animal organism was 

 but little understood, and their intrinsic relations to detinite 

 physiological processes, for obvious reasons, scarcely fcus- 

 ])ected. 



The classifications of the various articles of animal food 

 with reference to their relative feeding value, on the part of 

 leading physiologists of that time, furnish one of the most 

 striking illustrations of the change which has taken place in 

 that direction. A classilication of articles of food Avith refer- 

 ence to quantity and quality of their essential proximate con- 

 stituents did not exist ; the idea that some of these constitu- 

 ents might have to perform different functions in the animal 

 economy than others did not yet enter into their considera- 

 tion. 



A cursory discussion of the circumstances which led to the 

 recognition of the special functions of the principal constitu- 

 ents of plants in animal nutrition may serve as farther proof 

 of the great influence which chemistry has exerted on our 

 present notions of the relative nutritive value of our various 

 articles of fodder for farm animals. 



1. Nitrogenous Constituents of Food. 

 (Protein suljstances.) 



« r 



p I Albumen — Eggs, blood serum, plants. 

 H g ! Casein — Milk ; leguminous plants, beans, etc. ; legumen. 

 Ill Fibrin (solid) — Blood changes into it ;' gluten in wheat, etc. 

 £ I (They occur in the vegetable and animal kingdom.) 



« I 



The beginning of a better knowledge of the special rela- 

 tions of nitrogen-containing or2anic constituents of the ani- 

 mal food to animal nutrition may be traced directly to ex- 

 aminations of that class of substances by Mulder, Liebig and 

 his pupils from 1830 to 1840. Their extensive investiga- 

 tions of many of our farm plants proved, contrary to current 

 opinions, that all plants, and all parts of these plants, contain 



