276 THE VITAMINS 



disease very nearly coincides with the period in which the rat ceases 

 to grow and begins to lose weight. Of the 69 cases above, reported 

 by Osborne and Mendel, 33 showed eye symptoms at approximately 

 maximum body weight; 15 after a decHne of 10 to 20 grams from 

 the maximum; 13 after a loss of 20 to 30 grams; 8 after a loss of 

 more than 30 grams in body weight. The pathology of this eye disease 

 has been studied by Wason (1921). 



As the animals approach maturity their requirement for vitamin A 

 appears relatively less acute because of the fact that they can remain 

 in health for a longer time upon a diet deficient in this respect. In 

 how far this means a real diminution in the vitamin A requirement 

 and in how far it depends upon the fact that the older and larger 

 animal, if it has previously been well fed, has a larger store upon 

 which to draw in such emergencies is not entirely clear ; and the solu- 

 tion of the question is complicated and difficult because our usual 

 criteria become less serviceable as the young animal approaches ma- 

 turity, since growth has now nearly ceased and it is reasonable to 

 suppose that the conjunctival tissue will be less sensitive in an animal 

 which has made a normal growth and development than in the young 

 growing individual. Full grown rats when placed upon diets lacking 

 vitamin A are less likely to develop the characteristic eye trouble 

 than are young growing individuals; but, if the experiment is suffi- 

 ciently prolonged, eye trouble appears in a considerable proportion of 

 cases even of rats which had grown to maturity on good diets. 



As shown more fully below, the relation of the eye disease to 

 this dietary deficiency (lack of vitamin A) has been experimentally 

 demonstrated in several other species as well as rats, and special 

 interest attaches to the question as to whether the use of dietaries 

 poor in vitamin A may be a factor in the susceptibility to eye trouble 

 in man. Relatively early McCoUum (1918) wrote, "There are several 

 instances of the occurrence of conditions described in the literature 

 as xerophthalmia, which seem to be beyond question, cases in which 

 the disease has occurred in man as the result of specific starvation 

 for the dietary essential, fat-soluble A." The reports here referred 

 to are those of Mori (1904) in Japan whose cases of xerophthalmia 

 occurring among children at a time of food shortage could be cured 

 by feeding chicken livers (liver being rich in vitamin A) and those 

 of Bloch (1917) whose cases among the children of the Danish poor 

 also responded to the feeding of foods rich in the A-vitamin. Wells 

 found in Roumania, and Dalyell in Vienna, cases of children sufifering 

 from eye trouble which could be cured by cod-liver oil and presumably 



