VITAMIN A 289 



produce and rear young (Sherman and MacLeod, 1925; Batchelder, 

 1929). See Figs 13 and 14. 



By means of the methods developed by Evans and his coworkers 

 in the Department of Anatomy of the University of Cahfornia, Evans 

 and Bishop (1922) have thrown further light upon the significance 

 of vitamin A in relation to reproduction. As summarized by Evans his 

 studies "confirm the impression that rats may be successfully reared 

 on diets poor in vitamin A if the diet is not too deficient in this essential. 

 They may for months grow normally and not suffer from the so-called 

 xerophthalmia. It must be admitted that we have not previously had 

 a method for the detection of deficiencies in this vitamin which, never- 

 theless, permit fair growth and apparent health. Studies on the oestrous 

 cycles of such rats show that they may suffer from an invariable and 

 continuous abnormality or disfunction of the ovaries. It has previously 

 been shown in this laboratory that ovulation in the rat can be detected 

 in the living animal by a series of histological changes in the vaginal 

 smear, changes which are correlated with the growth, maturation and 

 rupture of the Graafian follicles at periodic intervals. When for any 

 reason the follicles are unable to completely mature (as in animals 

 treated with hypophyseal substance) vaginal oestrous changes are ab- 

 sent. A totally different picture is produced if follicles develop but 

 are unable to rupture; under such circumstances, the oestrous changes 

 may be remarkably prolonged, and the dioestrous pause in fact obliter- 

 ated. As Evans and Long have shown, this occurs as a rare anomaly 

 in large colonies of animals. But this prolongation of oestrous vaginal 

 changes and failure of ovulation occurs in 100 per cent of animals 

 reared on diets which are low in vitamin A but which have neverthe- 

 less permitted preliminary normal growth." 



Later, Evans ( 1928) stated that inadequate vitamin A supply char- 

 acterized by the constant appearance in the female of cornified cells 

 either predominantly or exclusively in the vaginal smear, injures the 

 female reproductive system so that fertilization and implantation usually 

 fail, even though oestrus and ovulation occur fairly frequently. 



In the above-mentioned work of Sherman and MacLeod (1925) 

 the comparison of the effects of a low versus moderately liberal intake 

 of vitamin A were not confined to observations upon reproduction but 

 extended throughout the lives of the experimental animals with results 

 which the authors have summarized as follows: "The smaller amount 

 of vitamin A proved sufficient for normal growth up to nearly normal 

 adult size, but not for successful reproduction, and rarely did it sup- 

 port satisfactory longevity. The parallel animals receiving the more 



