VITAMIN A 275 



means is doubtful, if allowance be made for the fact that on diets only 

 deficient in vitamin A and not devoid of it the animals not infrequently 

 show the eye trouble in some degree and recover spontaneously. Bulky 

 (1919) believed the eye trouble to be an infection controllable by sani- 

 tary precautions and local treatment with antiseptics, but Osborne and 

 jMendel (1921) found this not to be true in their cases, and Stephenson 

 and Clark (1920) have pointed out that the diets used by Bulley may 

 not have been so thoroughly freed from vitamin A as they were in- 

 tended to be. In their own experience, Stephenson and Clark report 

 the development of the eye disease in 13 of 46 rats kept on diets deficient 

 in vitamin A. Other investigators have recorded its occurrence in a 

 considerably larger proportion of cases. Emmett (1920) found it in 

 120 out of 122 such cases and in no case on other diets. Osborne and 

 Mendel (1921a), in a critical discussion of the subject, give the results 

 of an examination of their laboratory records of 1,000 rats representing 

 essentially the entire group under study in their laboratory during one 

 year. The rats were classified according to diet ; and the total numbers, 

 and numbers showing eye symptoms, were counted with the following 

 results : 



Incidence of Eye Disease in Osborne and Mendel's Rats. 

 (Nos. 5000-5999.) 



Total Number Number with 



of Rats Eye Symptoms 



On diets deficient in Vitamin A 136 69 



On diets deficient in Vitamin B 225 



On diets otherwise deficient 90 



On diets experimental but presumably adequate 201 



On mixed food (stock animals) 348 



1,000 69 



"From this summary it will be seen that although nearly one-half 

 of the thousand rats were on diets undoubtedly deficient, not a single 

 case of the eye disease was observed in animals other than those experi- 

 encing a deficiency in fat-soluble vitamin in the ration. The incidence 

 of the disease among this group is 50 per cent, somewhat higher than 

 that observed by Stephenson and Clark, and lower than that reported 

 by Emmett. It should be added that in observations on several thou- 

 sands of rats we have never observed distinct symptoms of comparable 

 eye disease in any animals except those which had experienced a de- 

 ficiency of fat-soluble vitamin in their diet."' 



Among animals on diets otherwise adequate but devoid of vitamin 

 A, the eye disease may occasionally appear before complete cessation of 

 growth occurs. ]\Iost frequently the first slight indication of the eye 



