INCIDENCE OF KERATOMALACIA AMONG RATS. 248 



In the totally deficient group — that is, in the firet six experi- 

 ments — keratomalacia supervened in 88-6 per cent, of the animals 

 under observation, two-thirds of the cases appearing before the 

 ()Oth day of the experiment, except in the case of the adult 

 animals. 



In the other group, 4'2"8 per cent, were affected, and two- 

 thirds of the cases appeared after the 60th day. 



It therefore appeam that the susceptibility of the animals and 

 the time of incidence of the disease vary directly with the amount 

 of Vitamin A in the fat under examination. Also, adult animals 

 are less susceptible to a deficiency of Vitamin A in the diet than 

 are young animals, since the symptoms of the disease were not 

 exhibited in these animajs until the 104tli to the 129th days, but 

 that nevertheless all four animals were affected and two ultimately 

 died. 



Further, it is interesting to notice the mortality among the 

 two groups. In the first group, 31 of the 39 affected animals died, 

 and in the second group 12 out of 24. These deaths all occurred 

 during the progress of the expeiiments. No further records were 

 kept of those animals which survived till the termination of the 

 experiments, so that it is possible that the mortalitj^ may have 

 been higher still. 



Attention is also drawn to the fact that in the partially- 

 deficient group most deaths occurred among the animals that had 

 the least amount of Vitamin A in the diet, as evidenced by the 

 growth curves recorded. 



The experiments on those fats in which a fair quantity of 

 Vitamin A was present showed no deaths at all and only four 

 cases of keratomalacia, all occurring late in the experiment, 

 among the 24 animals involved. 



Refekknces. 



' Stephenson and Clark, 1920. Biochem. Journ. 14, 502. 



^ Osborne and Mendel, 1921, Journ. Amer. Med. Assoc. 76, 905. 



3 Emmett, 1920, Science. 52, 157. 



* Stammers, 1921, Biochem. Journ. 15, 489. 



