REAL NUTRITIVE VALUE OF FOODSTUFFS 37 



One last item remains to be considered before we 

 can fully estimate the value of a foodstuff or ration, 

 and that is the proportion of the various nutritive con- 

 stituents in it relative to one another — in other words, 

 the balance of the food. Since proteins, fats, and 

 carbo-hydrates, have different uses in the body (a 

 certain minimum quantity of proteid matter being 

 essential for repair of waste, whilst the other two, heat 

 and energy producers, are largely interchangeable, so 

 that a deficiency in one can be made good by an increase 

 in the other), it is obvious that an economical diet will 

 require some balance between the nitrogenous and non- 

 nitrogenous constituents. The proteid, or albuminoid 

 part of a diet, is by far the most costly ; and although 

 proteins contain the essential elements (carbon, hydrogen, 

 nitrogen, and oxygen) needed to supply the body require- 

 ments, it is both practically and economically impossible 

 to feed an animal by giving protein alone. What the body 

 must have is a certain minimum quantity of nitrogenous 

 or proteid matter, and then its further requirements 

 of carbon and hydrogen can be supplied in the form of 

 the less costly fats and carbo-hydrates. Not only is it 

 necessary to have a minimum amount of protein and a 

 proportional amount of fats and carbo-hydrates in the 

 ration for a resting horse, but if any work is required 

 of the animal a proportionate extra quantity of food 

 has to be supplied to provide the necessary energy. At 

 first sight it might appear that any one of the three 

 nutritive constituents of food might be added to the 

 resting diet in sufficient quantity to supply this extra 

 energy ; but in practice it is again found that a certain 

 balance must be kept between the proteins, fats, and 

 carbo-hydrates. The balance, or ratio, varies with 



