in THE THEOEY OF HUMAN NUTRITION 101 



of physiological economy in nutrition and the minimum of protein 

 necessary for the adult man were published in London in 1905 in 

 a long monograph of 478 pages, fully illustrated with diagrams 

 and tables. They confirm the fundamental conclusion drawn from 

 the experiments on Fletcher, that the quantity of protein habitu- 

 ally taken is far in excess of what is really strictly necessary for 

 the adult man, and prove that this excess of nitrogenous substances 

 is not only useless, but injurious to the animal economy. 



These researches, which were carried out on a broad experi- 

 mental basis, lasted several months. Determinations were made 

 not only of the total quantity of nitrogen taken with the food and 

 discharged in the urine and faeces, but also the uric acid, 

 phosphoric acid, muscular and psychical activity, the relative 

 number of erythrocytes in\the. blood, the daily variations in the 

 weight of the body, and the general condition of the subjects of 

 the experiments. 



These persons belonged to three classes: the first group of 

 professional men was composed of five professors and assistants 

 of the University, Mendel and Chittenden himself being of the 

 number ; the second, of eight students, trained in gymnastic 

 exercises and athletics ; the third, of thirteen soldiers from various 

 American States. 



The main object of the researches was the reduction of the 

 quantity of protein to a minimum without disturbance of nitro- 

 genous equilibrium and the weight of the body ; in other respects 

 the subjects of the experiment had full' liberty in the choice of 

 food. The soldiers alone were not free to choose, but were limited 

 to the prescribed rations, and were obliged to take a smaller 

 quantity so as to reduce as far as possible the total quantity of 

 protein consumed daily. 



The total intake and output of nitrogen were determined daily 

 by Kjeldahl's method, after the total amount of food, urine, and 

 faeces had been weighed. 



The greatest difficulty found by Chittenden in these researches 

 was naturally the theoretical prejudice that at least 100 grins, of 

 protein must be consumed daily in order to preserve nitrogenous 

 equilibrium, and more especially the habit, which is deeply rooted 

 in every one, of indulging in a diet excessively and quite need- 

 lessly rich in such substances. It will be readily understood that 

 when men 'have been accustomed for generations to this lavish 

 regimen, they naturally experience, when they begin to reduce it, 

 a feeling of emptiness in the stomach and of general weakness 

 which makes them think it necessary to return to their accustomed 

 diet. It is therefore not surprising that about half the persons, 

 students and soldiers, who had allowed themselves to be experi- 

 mented on by Chittenden, could not stand the reduced diet pre- 

 scribed in his plan of research. This fact does not, however, 



