1877.] 



the Effect of Light on Bacteria fyc. 



499 



breaking the sealed capillary end within a ball of cotton wool. This tube 

 is still perfectly pellucid [Nov. 3]. 



"We concluded from this experiment that while three hours' vacuum 

 was insufficient to sterilize the solution employed, one of eight days 

 duration rendered it absolutely barren, the latter fact being confirmed by 

 several repetitions of the experiment, one of which demonstrated the 

 sterilization of the solution by two days' vacuum. 



On substituting urine for Pasteur solution different results were 

 obtained. 



Obs. 2. — A tube containing fresh acid urine was on September 19 ex- 

 hausted and sealed off. On September 22 the capillary point was broken 

 under cotton wool. On September 29 the contents were found to be 

 turbid with Bacteria. 



Having thus ascertained that urine resisted the sterilizing effects of a 

 vacuum for a period sufficiently long to enable us to test the effects of 

 insolation on this fluid in vacuo, we proceeded to carry out our original 

 plan of investigating the more intimate nature of the processes by which 

 light exerts its germicidal action. The result of this inquiry, so far as 

 it has gone, is shown in the following observation : — 



Obs. 3. Oct. 26. — Of eight test-tubes containing fresh acid urine, two, 

 which we will call aa, were simply plugged with cotton wool and insolated 

 in the ordinary way ; two, labelled a' a', were plugged and encased. The 

 four remaining tubes were exhausted at the Sprengel pump and sealed ; 

 two, bb, were exposed for insolation, the remaining two, b'b' } being encased. 



Oct. 30. — a'a' were both swarming with Bacteria. 



Oct. 31. — The exhausted tubes, both insolated and encased (bb and b'b') 

 were distinctly and nearly equally turbid, the degree of cloudiness being, 

 if any thing, more marked in the insolated tubes bb. 



The urine in the tubes aa, which were insolated in the ordinary manner, 

 contained numerous small points of submerged growing mycelium, but 

 with this exception was perfectly bright and clear. 



Nov. 2. — On examination with a T y immersion objective numerous 

 rods in active movement were seen in each of the four tubes which had 

 been exhausted. 



The tubes a'a' also swarmed with bacterial life ; their contents were 

 putrid and slightly alkaline in reaction. The contents of the exhausted 

 tubes had in each case a disagreeable putrefactive odour, but the reaction 

 was still acid. 



The urine in tubes aa was acid and fresh in odour. With the excep- 

 tion of numerous mycelial tufts and one or two moving rods in the 

 meshes, nothing was seen in these tubes on microscopical examination. 

 This experiment was a repetition of two previous observations which 

 gave similar results and need not be detailed. 



In all cases exhaustion at the Sprengel pump was carried on until 

 ebullition occurred in the liquid operated upon, and the mercury had for 



