292 THE VITAMINS 



Tentatively, the less complete data for longevity indicate a distinct 

 tendency toward longer life when the diet is richer in vitamin A. 



Urinary calculi were visible to the naked eye in rats on diets very 

 low in vitamin A ; but not in rats receiving no vitamin A at all, probably 

 because of their early deaths. Van Leer sum (1928) has reported micro- 

 scopical examinations showing urinary calculi and calcium deposits 

 present in 88 per cent of rats on a vitamin A-free diet. Evidently these 

 deposits are enabled to grow to macroscopic proportions in rats which, 

 though dying for lack of vitamin A, have had their life prolonged a 

 few weeks beyond that of negative controls. 



From these and other observations it is concluded that vitality is 

 affected in various ways by a deficiency of vitamin A, successive diminu- 

 tions of vitamin A in the diet first lowering the positive health and 

 then resulting in increasing evidence of nutritive failure. 



These results, therefore, confirm and extend the findings previously 

 recorded which had led to the conclusion, "that vitamin A is an even 

 more important factor in the chemistry of food and nutrition than 

 has previously been appreciated, for it must be supplied in liberal 

 proportion not only during growth but in the food of the adult as well, 

 if a good condition of nutrition and a high degree of health and vigor 

 are to be maintained." 



