CHAPTER III 



THE THEORY OF HUMAN NUTRITION 



SUMMARY. 1. Composition of the principal articles of food of animal and vege- 

 table origin. Theory of the normal diet for adult man, deduced from the statistics 

 of nutrition drawn up by Voit, Atwater, and Tigerstedt. 2. Criticism of the 

 statistical method. Experimental researches of Hirschfeld, Kumagawa, Klemperer, 

 Siven, Caspari, and Albu, proving that nitrogenous equilibrium can be maintained 

 on a diet considerably less abundant than that in common use. 3. Fletcher's case 

 scientifically illustrated by Chittenden. 4. Chittenden's recent experimental 

 researches on three groups of persons, proving the theory of reduced or economical 

 nutrition. 5. The question of vegetarianism. 6. Variations of diet i(i relation to 

 sex, the stage of growth (anaplasia) and old age (cataplasia). Bibliography. 



TAKING as our basis the results of researches upon exchange of 

 material, we were able to classify food substances in groups in 

 accordance with the criteria of physiology, that is, according to 

 their different uses in the organism (Chap. I. 12). In the 

 discussion on the exchange of energy of the whole organism we 

 ascertained the heat value of the principal organic compounds in 

 foods, the potential energy inherent in their chemical composition 

 (Chap. II. 1). We have therefore gained a fair knowledge of 

 the conditions on which the material and dynamic equilibrium of 

 the animal economy depends, and may venture to attempt the 

 solution of the difficult and at present much disputed problem 

 of the diet best suited to normal man at different ages, in different 

 occupations and under different conditions of life. It is an 

 eminently practical problem, of equal interest to the physiologist, 

 the hygienist, the doctor, and the sociologist. 



I. With regard to the diet required to keep a man in good 

 health, we may conclude from the results arrived at in the two 

 preceding chapters that he must take every day a certain quantity 

 and quality of food-stuffs suitable for the development, nutrition, 

 and restoration of the tissues (proteins) ; and containing a 

 sufficient quantity of potential energy for the exercise of the 

 various functions (fats and carbohydrates) and finally supplying 

 the right stimulus to the activity of the digestive organs without 

 tiring them unduly (condiments). 



In the choice of food, man and animals alike are, as a general 



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