VITAMIN D 309 



varying degrees of various sterols or of certain forms of those 

 sterols. 



Using the monochromatic mercury line at 265 jxn, Fosbinder, Daniels 

 and Steenbock (1928) found a minimum energy input of 234 ergs 

 necessary to activate sufficient "cholesterol" to give a positive test for 

 deposition of calcium in a rachitic rat. According to the quantum theory 

 the total radiation under the conditions of their experiments was 

 3.2 X 10^^ quanta. Assuming the Einstein photochemical relation, they 

 calculated that Z.2 X 10^^ molecules or 2 X 10"^ gram of vitamin D 

 (molecular weight of cholesterol, 385, assumed) is sufficient to give a 

 detectable deposition of calcium in a rachitic rat. 



Kon, Daniels and Steenbock (1928) studied the photochemical 

 formation of vitamin D from ergosterol under the action of mono- 

 chromatic light for different lines. They found the quantity of radiant 

 energy necessary to form an amount of vitamin D sufficient to cause a 

 demonstrable deposition of calcium in the bones of rachitic rats to be 

 quite constant over a wide range of radiations, 700 to 1000 ergs being 

 necessary for the 256, 265, 280 and 293 fifi lines, whether the ergosterol 

 was irradiated in the solid state or in alcoholic solution, and both for 

 ergosterol acetate and for ergosterol. The hydroxyl group apparently 

 plays no part in the activation. 



They also irradiated chemically purified cholesterols, purified by the 

 severe methods which Bills believes do not wholly destroy their activata- 

 bility and found that the highest amount of energy used, 200,000 ergs, 

 was insufficient to activate them. This caused them to conclude "that 

 ergosterol is at present the only substance known to be specifically 

 activated by radiant energy." 



In 1927 Rosenheim and Webster (1927e) had noted that exposure 

 of ergosterol to ultra-violet radiation produced a mixture of substances, 

 including vitamin D, and found evidence suggesting that for moderate 

 periods of irradiation, the amount of vitamin D present in the mixture 

 was nearly independent of the period of irradiation, apparently owing 

 to simultaneous formation and destruction of the vitamin. 



It had been suggested by Morton, Heilbron and Kamm (1927) and 

 also by Pohl (1927), that as vitamin D seemed to show absorption 

 chiefly between 230 and 260 //// while ergosterol shows it chiefly between 

 260 and 290 //,a, the use of a filter cutting off all rays of wave-length 

 shorter than 260 //// should increase the quantity of vitamin D formed, 

 by reducing its rate of destruction. Webster and Bourdillon (1928) 

 were unable to verify this hypothesis. These latter investigators 

 also irradiated ergosterol at temperatures varying from 77.8° to 



