26 



Prof. J. R. Green. Action of Light on 



that which several observers, especially Marshall Ward,* have 

 noticed it to have upon the life of micro-organisms and other lowly 

 forms of vegetation. 



The method of investigation has been to expose various solutions 

 •containing diastase to the action of light for several hours, either 

 that of the total spectrum or of selected portions of it, and after such 

 •exposure to test the hydrolysing power of the solutions upon a weak 

 solution of soluble starch or upon a 1 per cent, starch paste. Con- 

 trols have been carefully kept during each experiment, and so 

 arranged that any difference shown in diastatic power has been 

 •clearly attributable to the illumination. 



The diastatic solutions have been extract of malt; solution of 

 diastase precipitated from such extract by alcohol ; diluted human 

 saliva freed from mucin ; and extracts of foliage leaves. The solu- 

 tions have been preserved by the addition of 02 per cent, of potassic 

 cyanide. 



The source of illumination has been either bright sunshine, diffused 

 daylight, or the light from a powerful naked electric arc, access to 

 the latter having been obtained through the kindness of Mr. Barker, 

 the manager of the electric light works at Cambridge. 



The diastatic power has been ascertained by titrating the results 

 of the digestions with Fehling's fluid, combusting the filters with the 

 precipitates, and weighing the resulting cupric oxide. 



When all the rays of the spectrum were under investigation, the 

 diastatic extracts were exposed to the light source either in quartz- 

 fronted cells, or mixed with films of agar-agar, the former method 

 giving the most satisfactory results. 



From many repeated experiments it was found that exposure to 

 the whole of the spectrum for several hours caused the destruction 

 of from 20 to 60 per cent, of the diastase. 



When the ultra-violet rays were cut off by the use of glass vessels, 

 glass having been proved by many observers to be opaque to these 

 rays, the effect was different. At first and for some time there was a 

 very considerable increase in the diastase, but this was succeeded on 

 a prolonged exposure, lasting several days, by a gradual and almost 

 complete destruction of the enzyme. 



By the use of a series of screens, arranged according to the direc- 

 tions of Landolt,t the visible spectrum was divided into five regions : 

 red, extending from wave-length 720 fifi to 640 /(/* ; orange, 640 fifi to 

 585 /t/t ; green, 585 fijx to 500 fi/i ; blue, 500 /nfi to 430 ^ ; and violet 

 beyond 430 /ujli, and these several bands were examined separately. 



Details of the experiments are given in the complete paper. The 

 results may be stated in percentages. 



* 1 Phil. Trans.,' B, vol. 185, 1895. 



f ' Ber. d. Deut. Chem. G-esell.,' 1894, p. 2892. 



