Absorption Spectra Studies on Cholesterol and Ergosterol.*

In the previous paper it was shown that highly purified spinal cord cholesterol is still activatable to antirachitic activity when irradiated in the solid form by a Cooper Hewitt mercury vapor quartz lamp. Although the activatability is decreased by the purification methods employed, nevertheless these purified products can again be rendered at least 25 times more activatable if heated under the proper conditions slightly above the melting point of cholesterol. Inasmuch as provitamin D activity has been claimed to be due specifically to ergosterol (l-4) our results might be interpreted as due to the presence of or formation of ergosterol in our preparations and as it is well known that the absorption spectrum of ergosterol is a very characteristic one we considered it desirable to conduct absorption spectra studies on our products in order to obtain physical evidence for or against this interpretation. As a source of light the continuous radiation from hydrogen in the violet and ultra-violet region was utilized (5-7). The gas was contained in a Geissler tube of simple design (Text-fig. 1) so arranged that the luminous thread of the capillary portion was projected end on through a quartz window upon the slit of the spectrograph. The source tube contained pure electrolytic hydrogen at a pressure of about 15 mm. and was rendered luminous by excitation from the secondary of an open core transformer, the primary of which through a current-limiting rheostat was con-