262 SCIENCE REMAKING THE WORLD 



We are somewhat accustomed to quantitative ratings 

 of soundness and efficiency and much more so to data 

 of growth rates, birth rates, and statistics of duration of 

 life. In human experience so many factors may enter 

 to influence health in the course of a lifetime that it is 

 hard to separate and measure the effects of food alone. 

 But this can be done with laboratory animals of rapid 

 growth and early maturity like the rat, and in such ex- 

 periments it is possible to determine under conditions 

 uniform in all other respects the influence of food upon 

 the various factors of health comprised in the definition 

 just quoted. 



Among the recent findings of nutrition experiments 

 carried through successive generations of such labora- 

 tory animals the results of which are, I believe, directly 

 and fully applicable to the problem of the attainment 

 of the highest degree of human health, is the fact that 

 starting with a diet already adequate we may by im- 

 provement of the diet induce a higher degree of health 

 and vigour. This has been rather strikingly shown in 

 experiments with rats in which different families from 

 the same stock have been kept for successive genera- 

 tions upon two uniform food supplies : the first diet 

 adequate as shown by the fact that it has supported 

 healthy growth, development, and reproduction in 

 some families for no less than six generations; the 

 second diet differing from the first merely in that it 

 contains a higher proportion of milk. These experi- 

 ments are still in progress but certain results are already 

 clear. 



Among the evidences of a higher degree of health 



