46 M.cCOLLUM— RELATION OF DIET TO PELLAGRA. 



toxic or irritating products of the degradation of certain amino- 

 acids are absorbed in amounts sufficient to cause damage to the tis- 

 sues. It has been recommended that man should, in adult life, take 

 only such an amount of protein as will cover the endogenous loss 

 due to tissue metabolism, together with a not well-defined " margin 

 of safety." The opponents of this view regard a liberal protein 

 allowance as essential to vigor and aggressiveness, and point to the 

 use of liberal amounts of meat by the peoples who have been char- 

 acterized by greatest achievement. Among all the progressive peo- 

 ples of the world the food supply is derived to a greater or less 

 extent from daily products, and this portion rather than the meat 

 eaten we have come to regard as of peculiar importance in improv- 

 ing the quality of the diet. In order to test this question we con- 

 ducted a series of experiments, employing rats which were about 

 nine months old. or about one fourth through the normal span of 

 life for this species, and were in excellent nutritive condition. They 

 were fed diets which were fairly satisfactory in all respects except 

 that the protein content was not far from the actual amount re- 

 quired for the maintenance of body weight for a few" weeks. We 

 observed unmistakable signs that the vitality of the animals was rap- 

 idly lowered on such a dietary regime. This was shown especially 

 by the rapid aging and short span of life. Even though the initial 

 body weight was approximately maintained for a period of three 

 months or more, distinct signs of aging were always apparent within 

 five to ten months. Three months in the life of a rat correspond 

 to about 8.4 per cent, of the average span of life. It can be readily 

 appreciated that if harmful effects in corresponding degree follow 

 the adherence by man to such low protein diets they would not be- 

 come apparent within the time covered by any experiment yet con- 

 ducted upon a diet squad, few of which have been restricted to any 

 experimental diet beyond six months. A reputed satisfactory out- 

 come of such experiments cannot be accepted as evidence that men 

 on diets which furnish but a small margin of protein over the actual 

 maintenance requirements are so nourished as best to promote 

 health. Aging at two to four times the rate observed in the most 

 satisfactorily nourished would escape observation in any experiment 

 on man with which we are familiar. 



