814 NUTRITION AND HEAT REGULATION. 



determine the low limit for this equilibrium and to ascertain whether, 

 for the purposes of the best as well as the most economical nutrition, 

 this low limit is as good as or preferable to a higher amount of pro- 

 tein in the diet. Examination of the dietaries of civilized races 

 shows that, on the average, 100 to 120 gms. of protein are used 

 daily by an adult man. Voit gives 1 18 gms. of protein as the average 

 daily consumption. A variable portion of this amount passes into 

 the feces in undigested form, but we may assume that about 105 

 gms. are absorbed and actually metabolized in the body. Experi- 

 ments show, however, that a man may exist in good health upon 

 a much smaller amount per day, as little as 20 to 40 gms.,* provided 

 the non-protein portion of the diet is increased. The question is 

 whether the large excess of protein above what is actually necessary 

 for nitrogen equilibrium is beneficial to the body or is harmful, or 

 lastly is merely a waste, or, as the older physiologists called it, a 

 luxus consumption. The facts at our command at present are in- 

 sufficient to give a final answer to this question. On the pne side 

 we have the following facts: Some observers (Munk, Rosenheim), 

 from experiments made upon dogs, state that when a low protein 

 diet is maintained for some time the animals show a marked dis- 

 turbance in digestion and absorption, which may terminate in 

 death. The fact that mankind universally under the guidance of 

 the self-regulating appetite has adopted a high level of protein food 

 must also be given considerable weight. With our imperfect 

 knowledge of all the conditions it is dangerous to assert that this 

 outcome of the processes of natural selection is without important 

 significance. There is also the fact that in the modern treatment 

 of tuberculosis high feeding with proteins constitutes a factor to 

 which much importance is attributed. The inference seems to 

 be that such a diet increases the power of resistance of the tissues 

 toward invading micro-organisms. On the other side, we have the 

 evidence of numerous investigators, who have experimented upon 

 themselves, showing that a protein diet much smaller than that 

 ordinarily used suffices to maintain normal nutrition. Chittenden, 

 especially, in the careful work already referred to, has shown that 

 men in various walks in life, students, athletes, soldiers, may be 

 well nourished, without loss of strength or impairment of the feeling 

 of well-being, on a diet containing 30 to 50 gms. of protein instead 

 of 118 gms. These observers believe that the excess of protein 

 usually employed is undesirable in that it increases the amount of 

 injurious nitrogenous waste products, that it throws an unnecessary 

 amount of labor upon the excretory organs, and that it increases 

 the possibility of the formation of toxic products in the intestines 

 * Consult Chittenden, "Physiological Economy in Nutrition," New York, 

 1905, for discussion and literature. 



