406 NUTRITION. 



shall be able by establishing the relations of the most favourable 

 admixture of different articles of food, to keep the fats and carbo- 

 hydrates sufficiently separate, and to attempt to ascertain the propor- 

 tion between each individual element of nutrition and all the 

 others. For the present we must take the normal food which 

 nature itself has prepared for the infant organism as the standard 

 by which to judge of the most favourable proportions in the mixture 

 of nutrient substances. If we assume the mean constitution of 

 woman's milk to be that mixture of the four groups of substances 

 which is best adapted for the nourishment of the human organism, 

 we should find that the most nutritious food exhibits the propor- 

 tion of 10 parts of plastic matter, 10 parts of fat, 20 parts of sugar, 

 and 0'6 of a part of salts. 



In our investigation of the most favourable mixture of the 

 different nutritive matters, we must not forget that these rela- 

 tions change in accordance with the condition of the organism, for 

 the requirements of the body equally demand variations in the 

 composition of the food and in its absolute quantity. Even in the 

 consideration of milk, we are struck by the fact, that nature has 

 been careful to vary its composition in accordance with different 

 circumstances, whilst its proportions remain invariably the same 

 under perfectly similar circumstances. The proportion of the con- 

 stituents of this nutrient fluid, which nature provides for the suck- 

 ling which has just begun to breathe, is the same in every case, 

 but is quite different from that which is supplied to young animals 

 after they have breathed the air for a longer time. The propor- 

 tions in which the constituents of the milk occur are moreover 

 different for the different classes of animals ; cows' milk contains 

 relatively less sugar and more fat and casein than woman's milk ; 

 while asses' milk contains very little casein, but, on the other hand, 

 much sugar and far more fat. It cannot be denied that (as we 

 have already noticed in vol. ii, p. 337) the food which the mother 

 may happen to take exerts a certain influence on the proportion of 

 the constituents of the milk; but it may be readily shown by a 

 comparison of the investigations made in relation to this subject, 

 that there is for every species of animal a certain fixed proportion 

 between the constituents of this primary food. It would appear 

 obvious from these indications, that the requirements of the animal 

 organism, which are influenced by various more or less prepon- 

 derating agencies, must present differences in the admixture of the 

 necessary nutrient matters. The effect of different influences of 

 the external world, the higher or lower excitation of the individual 



