II. CHEMISTRY 161 



found no \dtamin D in two species of higher algae, Enteromorpha intesti- 

 nalis and Laminaria saccharina, but in Fucus vesiculosus they reported 

 sHght activity. They found provitamin D, hut no \'itamin D, in phytoplank- 

 ton oiL 



Darby and Clarke^ *^ investigated the floating brown alga, Sargassum, in 

 the area of its origin near the Tortugas Islands. Here in clear water under 

 the tropical sun enormous quantities of the weed develop. Masses of it 

 break away and drift into the Gulf Stream, in which it floats as far as Ice- 

 land. As it drifts along it becomes heavily infested with moUusks, shrimps, 

 and other invertebrates, and thus indirectly it is a major food of fish. 

 Sargassum free of foreign matter contains about 3 % of oil on the dry basis, 

 and this oil was reported to have an antiricketic potency of the same order 

 as some of the poorer fish liver oils. 



An especially interesting example of the natural occurrence of vitamin 

 D in the vegetable kingdom is found in the work of Scheunert et al}^"^ with 

 edible mushrooms. Four species were studied, and they showed a vitamin 

 D content of 0.21 to 1.25 I.U. per gram when grown in the absence of strong 

 light. One species, the common Agaricus campesiris, exhibited 0.21 I.U. per 

 gram when grown in a cellar, and three times as much when grown in a 

 meadow where light presumably was a factor. In these ergosterol-rich 

 plants, a minute fraction of the provitamin apparently is activated with- 

 out the agency of light. 



There is no evidence that vitamin D plays any role in plant physiology, 

 and it is not difficult to understand why it is seldom found in live plant 

 tissues. The lower, non-pigmented, non-photosynthesizing plants, which 

 contain much ergosterol, thrive in dark places and perish in the light. The 

 higher plants, containing relatively little provitamin, possess pigments 

 which presumably filter out the activating rays at the short end of the 

 solar spectrum. Even if the vitamin could be formed in the superficial 

 layers, plants could not store it, unprovided as they are with any system 

 for the translocation of lipoids. 



In the animal kingdom vitamin D is less rare than in plants, but it is 

 abundant only in certain fishes. In mammals it is found principally in the 

 milk and liver, and in birds in the liver and egg yolks. ^'*- These foods contain 

 from a fraction of a unit to several units per gram — only enough to make 

 them marginal sources of vitamin D for human nutrition. The amount can 

 be substantially increased Ijy irradiating the animals or adding vitamin 

 D to their food.^^^ 



The fact that mammals and birds are subject to rickets is proof that they / 

 cannot synthesize vitamin D. Except for occasional amounts gained by eating i 



1" H. H. Darby and H. T. Clarke, Science 85, 318 (1937). 



'" A. Scheunert, M. Sehieblich, and J. Reschke, Hoppe-Seyler's Z. physiol. Chem. 235, 

 91 (1935). 



