COMPOSITION OF THE COMMONER TISSUES 

 USED AS FOOD-STUFFS FOR ANIMALS. 



The principal constituents of all animal and vegetable tissues 

 consist of water, proteins, carbohydrates, fats and salts. In addition, 

 various other substances are present, which are grouped together, 

 under the term "extractives". Amongst the extractives are found 

 the decomposition products of the above three classes of compounds, 

 viz. amino acids, glucose, purines, urea, creatine, creatinine, etc. 



Animal tissues consist mainly of protein with fat and only traces 

 of carbohydrates. In vegetable tissues the amount of carbohydrate 

 preponderates and the amount of protein is small. Protein is 

 present in greatest amount in the legumes ; cereals also contain 

 fairly large quantities. Fruits and green leaves consist mainly of 

 water, nuts almost entirely of protein and fat (oil). The following 

 table shows the proportion of the various constituents in the commoner 

 tissues or food-stuffs : 



Mention must also be made of the substances, termed vitamines by 

 Funk, of unknown constitution, the absence of which in food-stuffs, e.g. 

 polished rice, produces the deficiency diseases scurvy, beri-beri, pellagra, 

 etc. 



Food-stuffs, especially milk and some animal fats, contain an un- 

 known compound which is necessary for the growth of animals. It 

 is removed from food-stuffs by treatment with alcohol and ether and 

 seems to be destroyed by prolonged heating. It is contained in the 

 fatty constituents and is free from nitrogen (Osborne and Mendel). 

 The constituents of eggs and of milk can maintain the early life 

 of animals, but no single food-stuff contains the proportion of these 

 substances which are necessary to maintain life in an adult ; consequently 

 a mixed diet is almost universally taken. 



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