THE INFLUENCE OF CHEMISTRY. 121 



ing the chemical composition of the particular fodder on 

 Ihand, are points of first importance when phmning a rational 

 and thus economical system of feeding for any particular 

 kind of fiirm stock. A better knowledge of what we feed 

 enables us to give a more judicious explanation of the results 

 of our feeding experiments; it teaches us best, also, how to 

 supplement our own fodder resources to meet the special 

 •wants of our farm stock. 



Careful investigations in stock-feeding have taught us les- 

 sons similar to those we have learned to appreciate in feed- 

 ing plants, or in the cultivation and the production of farm 

 ■crops. All our farm plants need nitrogen, phosphoric and 

 sulphuric acids, potassa, soda, lime, magnesia and iron ; 

 yet not two species of plants have been found which need 

 the same quantity of these substances during their entire 

 period of life, nor at any stage of their growth. No one of 

 the above-stated essential mineral constituents of plants can 

 replace another one to any extent without altering the char- 

 acter of the plant, or even endangering its life. Potassa 

 cannot take the place of lime, nor phosphoric acid that of 

 sulphuric acid. When lime is needed, a shovelful of that 

 substance is worth more than any quantity of the many times 

 more expensive potassa ; that particular mineral element 

 •which supplies an actual want of the soil is, for this reason, 

 from a physiological standpoint considered the most impor- 

 tant one for the production of the plant ; for without it the 

 remaining essential mineral constituents of plants, whatever 

 their quantity ma}'^ be, cannot make them grow. 



In regard to the growth and the support of our farm live- 

 stock, similar relations have been noticed. Actual feeding 

 experiments have shown that three groups of plaut constit- 

 uents (nitrogenous, non-nitrogenous, and mineral constit- 

 uents) are required to sustain successfully animal life. No 

 one or two of them, alone, can support it for any length of 

 time. In case the food does not contain digestible non-nitrog- 

 •enous substances, the fat and a part of the muscles of the 

 animal on trial will be consumed in the support of respira- 

 tion before its life terminates. In case nitrogenous constit- 

 uents are excluded, the formation of new blood and flesh 

 from the food consumed ceases, for the animal system is not 



