496 



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



solution. A tube containing some of tlie same Pasteur's solution was 

 encased in the usual manner and all were plugged with cotton wool. 



June 5. — The encased tube became turbid. 



June 8. — A tuft of mycelium appeared in the medium yellow. 



June 9. — The deep yellow became clouded with Bacteria. 



June 11. — Tufts of mycelium appeared in the faintly yellow. 



The tubes suspended in distilled water became sterilized, nor could 

 any thing save mycelial growths be discovered in either of the solutions 

 exposed to yellow light, with the exception of that suspended in the yellow 

 of deepest tint, in which Bacteria had appeared at an early period and 

 excluded the mycelium. This result we attribute to the apparent fact that 

 the less deep shades of yellow allow rays to pass which may at least check 

 the development of Bacteria, but are less potent in their influence on the 

 germs of the higher fungi, which accordingly develop the more readily 

 since they have not to struggle with the former for the mastery. By this 

 indirect influence, therefore, rather than by any special and direct action, 

 we explain the tendency of mycelium to spring up in yellow light. This 

 explanation, moreover, is in accordance with our deduction that, although 

 the mycelial fungi are injuriously affected by light, they are nevertheless 

 more resistant to its influence than Bacteria. 



The breaking down in Observation 13 of the tubes in the case of 

 window-glass is remarkable when contrasted with the survival of the 

 solutions in the blue case. We have, however, invariably found it a 

 difficult matter to sterilize an ordinary cultivation-liquid when a second 

 screen of glass was placed between it and the light. 



Early in the investigation it occurred to us that oxygen might be found 

 to play a part in the phenomena under observation. Tubes containing 

 solution A were therefore exhausted at the Sprengel pump and sealed off, 

 our intention being, in the first place, to observe the effect of insolation in 

 the absence of an atmosphere, filtered air being afterwards admitted. 

 To our surprise we found in a preliminary experiment that on breaking 

 the sealed points of the tubes under cotton wool, after the vacuum had 

 been maintained for two days, the solutions were perfectly sterilized and 

 could be preserved indefinitely. This fact (which, we have since been 

 informed, was stated by Professor Tyndall in the Transactions of the Eoyal 

 Society this year) cut off for the present this mode of approaching the 

 problem. 



The deductions which we draw from these simple experiments may be 

 summed up as follows : — 



1. Light is inimical to the development of Bacteria and the microscopic 

 fungi associated with putrefaction and decay, its action on the latter 

 organisms being apparently less rapid than upon the former. 



2. Under favourable conditions it wholly prevents that development, 

 but under less favourable it may only retard. 



3. The preservative quality of light, as might be expected, is most 



