CONSTITUENTS OF FOOD. 93 



is an abnormally large expenditure of bodily fat, which has to 

 furnish as far as it can, the actual energy required for the work 

 of the body and for the maintenance of internal heat ; but the 

 variation in the excretion of nitrogen in the urine is trifling, 

 until the store of fat has been practically exhausted, and then 

 a rapid waste of nitrogenous tissue ensues up to the time of 

 death. It therefore appears that the chief feeding value of 

 nitrogenous matter in the food is to build up tissue ; and that 

 of starch, sugar, and fat, to furnish energy to the body. This 

 conclusion as to the building up of tissue being the principal 

 office of nitrogenous food, is supported by the experiments 

 made by Sanborn and Henry on growing pigs ; for those which 

 were fed on food rich m nitrogen had larger muscles and 

 stronger bones than those fed on food rich in carbo-hydrates, 

 but poor in nitrogen. These deductions are amply borne out 

 by the results of practical experience ; for we all know that a 

 horse cannot undergo severe and prolonged exertion success- 

 fully, unless he has been fed for some time previously on a 

 highly nitrogenous diet, or, to use a stable expression, has had 

 plenty of corn " put into him." We also know that old horses 

 which have been at grass and without corn for some months, 

 take a long time to regain their former working condition ; 

 and that the best way to prevent them, when at grass, from 

 losing muscular strength and staying power, is to feed them 

 on a fair amount of corn. Supposing that a hard-working 

 animal has his muscles fully developed, he will manifestly be 

 in greater need of food which is rich in energy-producing 

 material, than of a diet rich in nitrogen ; especially when we 

 take into consideration the comparative permanency of 

 nitrogenous tissue. This statement would, I think, lead us 

 to the conclusion that highly nitrogenous foods, such as 

 beans and peas, are more useful for horses which are low 

 in muscle, whether they are at work or idle, than for hard- 

 worked muscular animals. 



