On Blood- Platelets. 



451 



of the water-soluble vitamin supplied. When a small amount of this 

 vitamin is given, xerophthalmia develops much earlier than when a large 

 amount is given. This statement refers to experiments in which the water- 

 soluble vitamin was supplied in the form of " marmite." 



Between the two extremes which we have described, all intermediate 

 conditions may be observed. These large variations in reaction to a with- 

 drawal of the fat-soluble vitamin make it, of course, very difficult ■ to 

 appraise the significance of any changes in tissues and organs which may be 

 observed. Many changes which can be seen and have been described must 

 be regarded as accidental. Tor instance, the failure in nutrition which 

 may occur is obviously not an essential feature, and is not necessary for the 

 onset of infective conditions. In connection with our previous work on the 

 relation between lymphoid tissue and nutrition, it is of interest to note that 

 there may be a considerable lymphopenia when the animals have shown the 

 " acute " effect and are in a poor state of nutrition ; but when the eye 

 condition develops in a well nourished animal, the lymphoid tissue is normal 

 and the lymphocyte count shows only a slight diminution. The only general 

 feature common to all rats which have been subjected to a fat-soluble 

 vitamin deficiency is a greatly diminished resistance to infection. 



We have dealt in considerable detail with the great variety in the general 

 conditions of animals on a vitamin A-free diet, because a lesion, if it is to be 

 considered specific to this deficiency, must be present in all these animals. 

 Further, the severity of such a lesion should be found to vary with the 

 extent to which the animal is affected by this vitamin deficiency. And, 

 lastly, the lesion should disappear when the deficient vitamin is supplied, 

 and the animal recovers as the result. 



We have found such a lesion in the great reduction in the number of blood- 

 platelets. We were led to look for a change in the platelets, because we 

 noticed an obvious change in the condition of the blood of rats kept on a diet 

 deficient in the fat-soluble vitamin. When the tail was cut for the purpose 

 of examining the red and white corpuscles, the blood flowed much more 

 freely than in a normal animal, and it was much more difficult to arrest the 

 bleeding. When a film was made, it was more difficult to obtain an even 

 spreading. There were no constant differences in the number of white 

 corpuscles or of the red corpuscles to account for this change, although, as 

 will be seen later, there may be, in advanced stages of the deficiency, a 

 distinct ansemia. But the diminished coagulability of the blood, as it 

 manifests itself by the difficulty of arresting the bleeding, sets in long 

 before the anaemia occurs. The essential importance of the platelets in 

 blood coagulation, which the previous observations of Cramer and Pringle (1) 



2 K 2 



