314 MASSACHUSETTS AGRICULTURE. 



the oxide of iron, besides smaller portions of carbonate of lime, 

 fluoride of calcium, and silicic acid. 



These observations are based upon numerous comparative 

 analyses of the principal constituents of the animal system, and 

 of the various kinds of food in use. The particular efficiency of 

 our most important articles of food have been besides — as is in 

 this case of controlling- importance — repeatedly tested by practical 

 experiments under varying, yet well-defined circumstances, for 

 the purpose of securing a reliable basis in regard to the decision 

 of the important question : In what actual relation do the 

 different constituents of our various articles of food stand to the 

 several functions, and the normal workings of the animal system 

 in general ? For many years past, physiologists and chemists 

 have advanced the following general conclusions, which in their 

 essential points are recognized to-day. 



First. — There exists an actual connection between the nitrog- 

 enous portion of our food and the formation of the animal 

 tissues, and the amount of muscular power which we are able to 

 exert. 



Second. — There is a certain relation between the amount of 

 non-nitrogenous, or so-called respiratory, compounds of the food 

 consumed, our respiration and the deposition of the fat within 

 our systems. The nitrogenous portion of our food has been 

 called the blood or flesh-forming part, and the non-nitrogenous, 

 the respiratory or fat-forming portion. A special adaptation of 

 the several proximate compounds, of which our vegetable and 

 animal aliments are formed, we fully admit: yet, in attempting 

 to construct tables for the representation of the comparative 

 value of our various kinds of food, it has been assumed quite 

 generally that all our common articles of food are to be rather 

 valued by their flesh-producing than by their respiratory and 

 fat-producing capacity. Hence their percentage of nitrogen has 

 been recognized, with some limitation, as the standard by which 

 their value as aliments ought to be decided. Judging from this 

 standpoint, the analytical results, for instance, of both the 

 Cheddar and the skim-milk cheese, — 



