1886.] Action of Sunlight on Micro-orcjanisms, §-c. 



19 



where the investigation was made.* At the Royal Observatory the 

 means of the maxima in the sun's rays were : — 



June 126-1° F. (52-3° 0.). 



July 143-0 F. (61-6 C). 



August 129-2 F. (54-0 C). 



It cannot be doubted that these tubes were often exposed to a tem- 

 perature of 140° F. (60° 0.), and on at least one occasion (July 27) to 

 160° F. (71° C). 



The incased tubes had for radian fc heat a somewhat greater 

 absorptive power than the bare glass of the insolated. For tempera- 

 tures below 100° F. (38° C.) this difference was comparatively slight ; 

 at 100° F. it was 4'5° F. (2-5° C). 



It is certain, therefore, that any deleterious influence of heat should 

 tell more on the incased than on the insolated. Yet at the end of 

 four months Bacteria appeared, retarded in development, it is true, 

 but still morphologically identical with the forms originally found in 

 similar solutions. 



I lay stress on these facts, because an Australian observer has 

 declared! that we, and Professor Tyndall with us, have mistaken 

 effects of heat for supposed effects of actinism. J 



But Dr. Jamieson's paper in abstract has gone the usual round of 

 German year-books and periscopic notes of English journals, until an 

 impression has arisen that there is no satisfactory evidence of inju- 

 rious influence of light on micro-organisms. I trust, therefore, to be 

 permitted a few words in reply. 



Dr. Jamieson insolated Cohn's solution in phials, and found that in 

 a short space of time bacterial development might thereby be entirely 

 prevented. But in some of his experiments he thought that he suc- 

 ceeded better in hot weather than in cool, and he failed to produce 

 any effect in diffused light. He asked himself, therefore, whether the 

 results he had noted might not have been, after all, due to heat. 



This was a very legitimate question, but, instead of solving it by 

 direct observation, he unfortunately recalled to mind experiments § in 

 which B. termo had apparently been killed by seven days' exposure to 

 45° C. (113° F.), by fourteen hours at 47° C. (116-6° F.), by three or 



* Greenwich. Lett. 51*28 K Long. 0-00. 



Chelmsford „ 51-44 N. „ 0*28 E. 



t Royal Society of Victoria. June, 1882. 



X We cannot dispense with some word such as this to connote energy not neces- 

 sarily coincident with effects either of solar heat or luminosity. In using it above, 

 I go a little further than Professor Tyndall, who has not, I believe, yet given any 

 opinion as to the form of radiant energy, except that it is not heat, which he found 

 to hinder bacterial development. 



§ " Eidam. Beit, zur Biol, der Pfl.," Heft iii, p. 208. 



