DIET OF ANIMALS. 195 



these different food-stuffs will be discussed when we consider the nutri- 

 tive value of foods. 



We may, however, here call attention to the fact that in an animal 

 in whom no excessive demands for work are made a proportion of one 

 part of nitrogenous to eight of n on -nitrogenous food-stuffs will be sufficient 

 to maintain the body weight. When, however, the animal is worked, 

 then the proportion between nitrogenous and non-nitrogenous food must 

 be increased from 1:5 to 1:3. The following table, after Liebig, shows 

 the proportion of nitrogenous to non-nitrogenous principles in some 

 of the most common foods : — 



Cows' milk, 1 : 2 to 1 : 4 



Beans and peas, 1:2 



Ox-flesh 1 : 1.7 



Pigs' flesh, 1:8 



Calves' flesh, 1:1 



Potatoes, 1:10 



Oatmeal, 1:5 



Wheat-flour 1 : 4.6 



Rye- and barley-meal, 1 : 5.7 



The aliment which is well adapted to nourish one species of animal 

 is not necessarily suitable for another. Thus, a vegetable food which 

 furnishes the maximum of its nutritive principles to a ruminant, which 

 is capable of perfect!} - dividing it and retaining it for a long time in its 

 complicated gastro-intestinal apparatus, will be of little value to such an 

 animal as a horse for the directly opposite reasons. Further, the food 

 which may be nutritive for an animal with a perfect masticatory appa- 

 ratus will be useless to one in whom the teeth have not appeared or have 

 been lost ; or it may serve for a beast of burden which has need of blood 

 and tissue producers, and not for a fattening animal, or a cow kept 

 entirely for milking. The alimentary ration must correspond to the 

 losses of the organism, and must, therefore, be proportionate to the work 

 done and the animal's size ; thus, a man under ordinary circumstances 

 requires 20 grammes of nitrogen and 330 grammes of carbon daily, rep- 

 resented by 1000 grammes of bread and 286 grammes of meat. The 

 horse needs 7500 grammes of hay and 2270 grammes of oats, representing 

 10 kilo of hay and 2 kilo of oats for every 100 kilo of body weight. Loss 

 of weight occurs if this daily ration is reduced only one-tenth. For the clog 

 40 grammes of meat are necessary for each kilo of body weight, and here 

 also the animals lose flesh if these rations are decreased only one-tenth. 

 If the bodily losses are increased by work or by the secretion of milk, 

 or if the animal is in the growing period, when the size and weight of the 

 body should increase, it is also indispensable that these rations should 

 increase. In cases where extraordinary demands are made on the forces 

 of the animal, as in beasts of burden, the supplementary foods are then 

 to be given in small volume, and should then be of extremely nutritive 



