580 IX. CAROTENOIDS AND VITAMINS A 



I.U./day/kg. body weight, the minimum level required to prevent vaginal 

 cornification (as determined by vaginal smears)®''^'^**'^*^ was found to be 18 

 to 22; to avoid gross and histologic evidence of deficiency, 20;^^° to ensure 

 growth, 80;*^" for adequate growth, longevity and tooth color, 100;^^^ for 

 optimum growth, 25;^^'' for minimum liver storage, 50 to 80;^^^ for adequate 

 Hver storage, 100;^^" for maintenance of normal blood levels, 50.^"" 



When the daily requirement was based upon I.U./IOO g. of food, growth 

 was found to require 20"^ and 40;^^^ and optimum longevity, i^200.^*^'^^^'^''° 



When the basis of the vitamin A requirement of the rat was the amount 

 (in I.U.) needed per whole rat per day, the results also presented wide 

 variations, according to the procedures employed, viz., liver storage, 

 12969 and 100;^^" blood level, 20^^^ and 50;^^" growth j^^o cure of xeroph- 

 thalmia, 4;^^^ and tooth color, 3.^^^ 



As an illustration of the data upon which the above estimates of the vita- 

 min A requirements of the rats are based, one may observe the effect upon 

 growth of different amounts of vitamin A, as shoAvn in Figure 3. 



Table 9 



The Relation of the Vitamin A Intake of Rats 



TO THE Vitamin A Content of Plasma, 



Liver, and Retina" 



« Adapted from J. M. Lewis, O. Bodansky, K. G. Falk, and G. McGuire, J. Nutrition, 

 23, 351-363 (1952). 



Other experimental data which have been employed to assess the vita- 

 min A requirement of rats, based upon blood level, liver storage, and the 

 concentration of vitamin A in the retina, are given in Table 9, while Table 

 10 summarizes the relationship of life span to vitamin A intake. 



9™ H. C. Sherman and H. L. Campbell, Proc. Nat. Acad. Sci., U. S., 31, 164-166 

 (1945). 



