THE COW PEA. 43 



and support of bone, blood, nerves and muscles. These 

 constituents of food are grouped under one heading and 

 are Icnown as ' The Ash." Second, materials which contain 

 nitrogen. These are converted into lean meat, skin, hair, 

 the casein and albumen of milk, etc., and are termed by- 

 chemists the " Proteins." Third, sugars, starches, oils, fats 

 and similar materials, often classed chemically as "nitro- 

 gen free" and "ether extracts" — " Carbo-Hydrates." 



These three, "ash, protein, and carbo-hydrates," vary in 

 degree of digestibility, which is also affected by the source 

 whence each is derived. Generally speaking, fats and 

 sugars are more easily digested than starches or proteins — 

 grain, than hay; hay, than straw. In addition to the needs 

 enumerated is that of heat and energy for the animal body, 

 which gets its glow and power, as does a steam engine, by 

 the consumption of carbon. For producing this heat and 

 energy, "fats" and "ether extracts" are about two and 

 four-tenths times more effective, pound for pound, than 

 starches, sugars and other "nitrogen-free" materials, that 

 is 2.4 times the digestible parts of each and not their total 

 amounts. This may be stated in the form of a working rule. 

 Ascertain the chemical and digestible composition of the 

 food under investigation and multiply the amount of digest- 

 ible fat by 2.4, and to the product add the amounts of fibre, 

 starch, etc., (" nitrogen-free extracts"). The sum shows 

 approximately the digestible carbo-hydrates contained, 

 which divided by the digestible proteins gives the relative 

 value or ratio of these two. This subject is extensively 



