454 Messrs. W. Cramer, A. H. Drew, and J. C. Mottram. 



little further general comment. In the weight curve of each rat the arrow 

 indicates a count, and the number attached to the arrow gives the number of 

 platelets in thousands. Thus " 217 " means 217,000 platelets per cubic milli- 

 metre. The onset of eye symptoms is indicated by " x." More advanced 

 stages are indicated by "xx" and " xxx." In the figures which illustrate 

 the recovery from the vitamin A deficiency, the broken line represents the 

 weight curve during the last weeks of the absence of the vitamin, the full line 

 gives the weight curve after the addition of this vitamin in the form of cod- 

 liver oil. Most of these recovery curves refer to animals dealt with in the 

 preceding figures, as will be evident from the rat numbers attached to each 

 curve. In these recovery curves the sign Q stands for the complete disap- 

 pearance of the xerophthalmia. 



The figures illustrate all the different varieties of conditions which can be 

 observed in rats when kept on a diet deficient in vitamin A. Special attention 

 is drawn to fig. 1, which refers to an experiment specially devised to illustrate 

 the two extreme conditions and the parallelism between the effect of the 

 vitamin deficiency on the general condition of the animals and on the 

 platelets. 



In this experiment two groups of three rats derived from two litters, X 

 and Y, were taken. The litters were born within three days of each other. 

 The mother of the litter X had been kept during pregnancy and lactation on 

 the ordinary laboratory diet of bread and water, rice and maize. This diet 

 was continued for the young rats after they had been weaned until the actual 

 experiment began. The mother of the other litter, Y, had been kept on the 

 same diet, to which an ample supply of vitamins A and B had been added in 

 the form of cod-liver oil and marmite, and this diet also was continued for the 

 young rats. 



When the rats were 7 weeks old, the three heaviest and healthy- look in g 

 of each litter were selected, and the six rats placed together in one cage and 

 fed with the vitamen-free basal ration (purified casein, starch, olive oil, salt 

 mixture), to which an ample supply of vitamin B was added in the form of 

 crude marmite. As fig. 1 shows, the rats derived from litter X stopped 

 growing almost at once and developed the typical eye infection within 8 or 

 9 weeks. Those of litter Y continued to grow fairly well at first. After the 

 eleventh week their weight became stationary and remained so for the next 

 6 weeks (at the time of writing). Up to that time they had not developed 

 any lesion or other infective conditions. They looked perfectly healthy 

 normal rats in a good state of nutrition, and formed a striking contrast with 

 the small, thin, infected rats of litter X. It may be added that the same 

 result was previously obtained in a similar experiment, while in a third such 



