206 



Messrs. A. Downes and T. P. Blunt on [Dec. 19, 



corresponding quantity of uninocnlated syrup being kept to ascertain 

 if any hydration occurred spontaneously. 



September 6th. — The uninocnlated syrup has no perceptible reducing 

 action on Fehling's solution, but the contents of all the vacuum-tubes, 

 whether insolated or incased, have produced hydration of the cane- 

 sugar, and there is no practical difference between their effect — as 

 measured by Fehling's solution — and that of the non-Sprengelised 

 zymase preserved in the dark. At the same time the corresponding 

 solutions of zymase insolated without previous exhaustion have very 

 feeble action indeed. We conclude, therefore, that, as in the case of 

 the oxalic acid, the destructive action of light is by oxidation, for, 

 while the zymase exposed to light and air was greatly enfeebled, a 

 similar solution in vacuo, although equally insolated, retained its energy 

 apparently unimpaired.* 



In proceeding to investigate the nature of the action of light upon 

 living organisms, we were met by difficulties, arising from the relation 

 of these organisms to oxygen, which for some time baffled our research ; 

 but these difficulties we have, we believe, sufficiently overcome to be 

 enabled to indicate the fundamental identity of the action of light upon 

 living organisms and upon the typical non- vitalised organic substances 

 selected for our previous experiments. 



In a postscript appended to our previous communication we stated 

 that in sealed tubes containing urine, which had been exhausted at a 

 Sprengel pump, organisms appeared in incased and insolated tubes 

 alike. 



We have made many repetitions of these experiments, and we have 

 invariably found that, whenever organisms appeared in the incased 

 exhausted tubes, they were simultaneously present ir equal amount 

 and vigour in the insolated, contrasting with the difference in beha- 

 viour between corresponding insolated and incased non-exhausted 

 tubes. 



It seemed, therefore, that in absence of an atmosphere, light (not- 

 withstanding the manifest enfeeblement of life brought about by the 



* It was our original intention to examine a large number of organic bodies, and 

 to ascertain to what extent this phenomenon of oxidation under sunlight occurred in 

 different classes of organic compounds. The recent researches of M. Chastaing 

 (" Ann. de Chim. et de Phys.," [5], t. xi) have anticipated us in this. M. Chastaing 

 experimented on such organic compounds as essence of turpentine, essence of lemon, 

 ether, oils, &c, all of which were oxidised in sunlight, the oxidation occurring in all 

 parts of the risible spectrum, but haying a maximum in violet and a nunimum in 

 red. It is noteworthy to observe how this distribution of the function of oxidation 

 of these substances in the spectrum, according to M. Chastaing, corresponds with 

 that assigned by ourselves on entirely independent grounds to the destructive action 

 of light on Bacteria. We should have stated, also, that, according to our experi- 

 ments, the oxidation of oxalic acid was very active behind blue glass, but feeble 

 behind red. 



