520 Agrimltural Chemistry. — Pig Feeding. 



Before considering the results themselves given in these 

 Tables, it may be as well to say a few words on some of the 

 questions of interest upon which, we think, they are calculated to 

 afford some useful information. 



Our readers are aware, that much attention has of late years 

 been paid to the subject of the adaptation of food, according to its 

 composition, to the various exigencies of the animal system. 

 And, it will be admitted, that it is to the experiments and writ- 

 ings of MM. Boussingault, Liebig, and Dumas, that we must 

 attribute, either directly or indirectly, much of the progress that 

 has been made. These writers, as well as many others, whether 

 themselves experimenters, or more systematic writers on the sub- 

 ject of the Chemistry of Food, seem with few exceptions, and with 

 some limitations, to agree on two main points, namely — as to the 

 relationship of the nitrogenous constituents of food, with the 

 formation in the animal body of compounds containing nitrogen — 

 and as to the general connection of the non-nitrogenous consti- 

 tuents with respiration and the deposition of animal fat. Founded 

 more or less upon this broad classification of the constituents of 

 food, according to their supposed varied offices in the animal 

 economy, a vast number of analyses of foods have of late years 

 been made ; and from the results of these analyses, numerous 

 Tables have been constructed, professing to arrange the current 

 articles of diet, both of man and other animals, according to their 

 comparative values as such. In attempting to apply to practice 

 the more generally admitted facts to which we have referred, in 

 the construction of Tables of the comparative values of foods 

 according to their composition, it seems to have been generally 

 assumed, that our current food-stuffs are thus measurable rather 

 by theiv flesh-forming than by their more specially respiratory and 

 fat-forming capacities. Hence, Avith some limitations, the percent- 

 age of nitrogen has always been taken as the standard of comparison. 



Founded on their per-centages of nitrogen, M. Boussingault 

 first arranged Tables of the comparative value of different articles 

 of food, chiefly in reference to the dieting of the animals of the 

 farm. And, in reference to the views and experiments of M. 

 Boussingault on this subject. Baron Liebig, at p. 369 of the 

 Third Edition of his Chemical Letters, makes the following 

 observations: — ''The admirable experiments of Boussingault 

 prove, that the increase in the weight of the body in the fattening 

 or feeding of stock (just as is the case with the supply of milk 

 obtained from milch cows), is in proportion to the amount of 

 plastic constituents in the daily supply of fodder." In like 

 manner various specimens of flour and of bread have been 

 arranged by Dr, R. D. Thomson ; other articles of vegetable diet 

 by Mr. Horsford ; and a large series of aliments from the animal 

 kingdom by MM. Schlossberger and Kemp. Dr. Anderson also, 



