490 Dr. A. Downes and Mr. T. P. Blunt on [Dec. 6, 



Ohs. 3. May 30. — Two tubes were partially filled with Pasteur's solu- 

 tion (Appendix, B). Both were plugged with cotton wool. One was 

 encased in paper, the other left bare. 



June 5. — The encased tube was quite turbid. 



June 12. — The bare tube, which had remained perfectly clear, was 

 now encased, and continued quite free from turbidity up to June 21. 



June 28. — Solution quite clear, but small tuft of mycelium growing 

 at bottom. 



July 7. — Examined with a high power. Mass of matted mycelium ; no 

 Bacteria or other living organisms seen. 



July 11. — The solution now teems with Bacteria, having doubtless 

 been impregnated by the dipping-rod used on July 7. 



Ohs. 4. May 30. — Two tubes containing unboiled Pasteur solution 

 (Appendix, A) were plugged with cotton wool, capsuled, and insolated 

 until June 21, when both were encased in the way previously described, 

 the plug being withdrawn from one, and the lead capsule replaced. 



Both tubes remaining clear up to July 2, the unplugged one was im- 

 pregnated by means of a glass rod dipped in a solution containing 

 abundant Bacteria. 



July 4. — The impregnated solution is distinctly turbid. The plugged 

 tube has remained perfectly clear up to the present date [October 11th]. 



Prom these observations we conclude that so far as Bacteria are con- 

 cerned the solution may be absolutely and perf ectly sterilized by sunlight. 

 It is important to note, however, that in Observation 3 the germs of a 

 fungus had apparently survived an amount of insolation which was fatal 

 to the development of Bacteria. This interesting point will be further 

 investigated in the sequel. 



Ohs. 5. May 5. — Two of the tubes used in Observation 1 were taken; 

 the contents of the one (encased) were turbid, and the other (bare) per- 

 fectly clear. The contents were well mixed, and divided between the two. 

 They were then exposed as before. 



May 8. — The contents of the encased tube are much the more turbid, 

 those of the bare tube are but slightly, if at all, more turbid than on 

 May 5th. 



This experiment tends to indicate that not only is light inimical to the 

 original development of the individual, but also materially retards the 

 rate of increase, even when the organisms are present in a matured con- 

 dition. The next observation was designed as a crucial test of this. 



Ohs. 6. July 10. — Seven tubes containing Pasteur's solution (A) were 

 inoculated with a glass rod dipped in a solution teeming with Bacteria, 

 care, however, being taken not to impair the translucency of that in the 

 tubes in question. Six of these tubes were then insolated, the seventh 

 being encased. The encased tube became turbid on July 14, the rest 

 remained perfectly clear. 



