1886.] 



Action of Sunlight on Micro-orga?iisms, fyc. 



17 



" qu'on pent aclresser aux experiences tres bien conduites, du reste, 

 et tres interessantes de M. A. Downes." (" Proe. Roy. Soc," vol. 26, 

 p. 488, 1877.) 



As regards the earlier of our memoirs, to which M. Duclaux refers, 

 this criticism is just. At that date knowledge of revivification of 

 germs in different media was neither so generally diffused nor so 

 precise as it now is. This advance we owe not least to Professor 

 Duclaux himself. Accordingly, in our first experiments we regarded 

 non-appearance of life in our insolated tubes of Pasteur solution, or of 

 urine, as proof of destruction of the organisms which they had ori- 

 ginally contained. In our second and more complete memoir, how- 

 ever, we reserved our opinion on this point. 



But it was an essential principle of the method on which we worked, 

 and the key to our success, that our nutrient fluids should be suffi- 

 ciently resistant to bacterial growth to hinder the development of 

 organisms, through the night, or during cloudy days, from outrunning 

 the inhibitory effects of insolation. It would probably, for example, 

 not often be possible to secure in England the results which Tyndall 

 obtained on the Alps with apparently considerable bulks of very 

 putrescible materials. Pasteur solution and the like are at their best 

 but limited media of nutrition ;* yet under special circumstances, as, 

 for example, in the demonstration of the action of diffused daylight 

 given beiow, it is necessary to largely increase their resistance to 

 decomposition. 



Moreover, the question whether the germs in our solutions were or 

 were not actually dead, does not affect the truth of our induction. I 

 cannot put this more pithily than has Professor Duclaux himself, in 

 a very courteous communication with which he has favoured me. 

 " You have clearly shown," he says, " that an insolated germ is a sick, 

 sometimes very sick, germ ; death is but a step further, "f 



It was an a priori probability that micro-organisms should vary 

 considerably in their powers of resistance to the oxidising influences 

 of light. In our previous papers, indeed, we gave examples of this 

 in the frequent survival over Bacteria of some less sensitive form of 

 Saccharomyces or Mucedo. 



I have lately met with an instance which may be worth recording, 

 as it enabled me to isolate a Bacterium of which I can find no previous 

 description. In each of a number of thickish glass tubes I had sealed 

 up 3 c.c. of distilled water, together with a small bulb containing an 



* For prolonged insolation I have for another reason quite abandoned their use. 

 They are liable to take on a brown coloration in sunshine, and I have had, in con- 

 sequence, to abandon a laborious series of experiments. 



f M. Duclaux tells me that he has also confirmed our observation that the 

 diastases are destroyed by sunlight. He operated on the diastase presure, the 

 coagulating principle of rennet. 



VOL. XL. C 



