SCIENCE AND PRACTICE OF FEEDING 221 



a certain amount of brick or stone, lime and sand, so 

 does a beast, in the building up of its body, or in the 

 manufacture of such products as milk or wool, require 

 each of the particular food ingredients mentioned 

 above for the purpose. 



We can carry the analogy still further. The brick- 

 layer or stonemason will require brick or stone, lime 

 and sand in certain proportions. If, for instance, he 

 has sufficient lime and sand for the making of the 

 requisite amount of mortar for 20 rods of a wall, and 

 only sufficient stone or bricks for 10 rods, then the wall- 

 building must cease when the 10 rods is erected, until 

 a further supply of building material is obtained. In 

 like manner a beast must have the proteins, oils, and 

 carbohydrates in certain proportions for its proper 

 nourishment. 



Now, if the builder has a sufficient supply of brick 

 or stone, but a deficiency of either sand or lime, he 

 can continue building an inferior type of wall — a dry 

 wall — without the lime. In like manner a beast fed 

 on albuminoids and carbohydrates, but without the 

 third ingredient, oil, can continue living and even 

 increase in weight, because the carbohydrates and fat 

 are interchangeable. 



Again, a beast can be fed — but not economically — 

 on albuminoids and fat without carbohydrates. Like 

 the building of the dry wall the results of feeding on 

 two foods, though, are not as good as when the three 

 substances are available. 



Without either sand or lime a perfectly dry wall 

 can be erected with brick or stone alone, and in like 

 manner a beast can — again not economically — be fed 

 for a time on pure albuminoids. This is because the 

 albuminoids can fulfil the functions of both fat and 

 carbohydrates, but the point to be especially remem- 



