II. CHEMISTRY 171 



min D but no vitamin D, whereas that taken in midsummer showed both 

 provitamin and vitamin. Their data are interesting in view of the July 

 change in vertical distribution of zooplankton described by Russell. ^**^ Cop- 

 pingiss demonstrated the presence of small amounts of vitamin D in cope- 

 pods collected in summer. Of the larger marine invertebrates, it may be 

 noted that the body oil of squid showed about 6 I.U. of vitamin D per gram 

 in a test reported by Bills.^^"'" 



Clear sea water is sufficiently transparent for the activating rays of the 

 sun to reach a depth of about one meter. ^*^' i*" It is therefore possible, and 

 in view of Belloc's work even probable, that in the smaller zooplankton 

 where the body area is large in relation to the volume, some vitamin D is 

 formed by insolation. It is unlikely that any significant amount of vitamin 

 D is formed by the insolation of fish or of the larger invertebrates, for most 

 of these species do not inhabit the top meter of the sea. The basking shark, 

 Cetorhinus maximus, is an exception in that it basks for hours at the sur- 

 face, feeding on little fish and plankton; yet its liver oil is poor in vitamin 

 D, even for an elasmobranch.^^^ The common goldfish, Carassius auratus, 

 which feeds in shallow pools, accumulates hardly a trace of vitamin D in 

 its body oil.^^^'^ River catfish, Icialurus pundatus, when experimentally ir- 

 radiated, proved very sensitive to ultraviolet rays, but even after many ex- 

 posures did not accumulate more vitamin D than catfish not irradiated,'^"'^ 



The suggestion that vitamin D may be synthesized by fish was first made 

 by Bills^*"'' in 1927. He observed that during the first four weeks of the 

 summer fattening season the cod of the Newfoundland shore fisheries 

 gorged themselves on a little fish called capelin, Malloius villosus, and that 

 during this time the oil content of their livers doubled without diminution 

 of vitamin D potency. It was roughly estimated that the capelin eaten 

 could not account for all the vitamin D accumulated, and the balance was 

 attributed to synthesis. In view of the later work of Pugsley and others, 

 the original premises may have been faulty, in that they did not contem- 

 plate the possibility that the cod population may have involved different 



"7 F. S. Russell, Nature 126, 472 (1930). 



188 A. M. Copping, Biochem. J. 28, 1516 (1934). 



189 W. R. G. Atkins and H. H. Poole, Trans. Roy. Soc. (London) B222, 129 (1933); 

 H. H. Darby, E. R. F. Johnson, and G. W. Barnes, Carnegie Inst. Wash. Publ. 

 475, 191 (1937). 



i»»N. G. Jerlov, Nature 166, 111 (1950). Jerlov's claim that effective radiations 

 penetrate to a depth of 20 meters was based on the use of light filters centering 

 on 310 m)u. One suspects that the radiations detected at this depth represented 

 leakage at the long wave side of the pass band. 



"' S. Schmidt-Nielsen and S. Schmidt-Nielsen, Hoppe-Seyler's Z. physiol. Chem. 

 189, 229 (1930). 



"*» C. E. Bills, unpublished observation. 



