VITAMIN D 331 



either in a difference in the degree of intensity of ultra-violet rays from 

 the sun and from an artificial source, or to the rapid removal or de- 

 composition of any antirachitic substances that might be produced in 

 the growing leaf. The opinion of the botanist that ultra-violet light is 

 possibly harmful and certainly unnecessary to the thriftiness of the 

 plant lends support to the latter theory. No one seems to have yet 

 studied the permanence of activation by ultra-violet irradiation of the 

 vitamin precursor in an uncut and growing plant. 



Leigh-Clare (1927a) was unable to demonstrate the presence of 

 vitamin D in the diatom, Nitsschia closterium. It is possible that the 

 amounts fed were not large enough to demonstrate the presence of 

 the vitamin — the largest, 0.46 gram daily (fresh weight), may be too 

 small to prevent, or effect a cure of, rickets in rats on the McCollum 

 diet No. 3143. 



It is, of course, possible that the plankton and small fish might 

 receive sufficient solar irradiation to activate the vitamin precursor, and 

 thus become a food source of vitamin D to the larger fish, including 

 the cod. But from his knowledge of their dietary habits and the vita- 

 min D content of their food, Bills (1927) calculated that codfish 

 would have to eat 26 times their weight in caplin in 4 weeks during 

 the fattening period, if food is the sole source of antirachitic vitamin. 

 He doubts if the cod eat to that extent. He also cited experiments in 

 which he fattened catfish on raw veal muscle (the fat of which had 

 no apparent antirachitic value when fed at a level of 4 per cent to 

 rachitic rats). The oil extracted from these fish was of normal or 

 enhanced potency. Of this work he says, "In evaluating this additional 

 evidence of the endogenous origin, one should, of course, consider the 

 remote possibility that the veal muscle contained undetected traces of 

 vitamin D which the fish with great economy might have salvaged." 

 Furthermore he found that 5 minutes of irradiation every other day 

 applied to fish under 20 centimeters of water not only did not increase 

 the antirachitic potency of the oil, but exerted a very deleterious effect 

 upon the health of the fish. Bills inclines to the theory that at least some 

 vitamin D is synthesized by fish. 



It is entirely possible that there are enzymes which can activate 

 the vitamin precursor, just as Bills (1926) has shown that antirachitic 

 substances can be formed by the action of a catalyst, floridin, on 

 cholesterol or tricholesterol in carbon tetrachloride. There is also the 

 possibility that for fish the longer light rays are antirachitic (produc- 

 tive of vitamin D). Van Leersum (1924) has shown that the injection 

 of hematoporphyrin in rachitic rats had a therapeutic effect on rickets. 



