1877.] 



the Effect of Light on Bacteria fyc. 



493 



(2) In a dull light : 



I. became turbid with Bacteria, July 26 



TT OQ 

 J - J -' 5J JJ ?J •)■) 55 ^° 



HI. „ „ „ „ „ 29 



IV. contained a tuft of mycelium, Aug. 2, and became 

 turbid with Bacteria and mycelium, &c, Aug. 5. 



(3) In diffused daylight : 



I. contained Bacteria J uly 29 



Hi 



III- > remained clear. 

 IV. J 



It is right to state that the tubes of series 3 were inadvertently 

 exposed to about twenty minutes of sunlight on July 24th ; but we do 

 not think that this materially interfered with the result, which demon- 

 strates the preservative influence of diffused daylight alone, although in 

 less degree than that of the direct solar rays. 



The greater tendency of the more dilute solution to decomposition has 

 been pointed out. "We have again and again endeavoured to sterilize a 

 solution one tenth of the strength given in the Appendix {A), but without 

 success. Whether this failure was due to the unfavourable state of the 

 weather and clouded skies which have invariably supervened, or whether 

 in a solution of this strength the development of the Bacteria proceeds 

 with such rapidity that a warm night may in its favouring tendencies 

 outbalance the retarding influence of the day, we cannot say. We have, 

 however, notwithstanding one or two failures in dull, close weather, 

 repeatedly succeeded in sterilizing urine, and have at the present time in 

 our possession tubes containing that liquid which has been preserved 

 perfectly fresh and clear through the summer months. 



One example is given. 



Obs. 10. July 26. — Three test-tubes were partially filled with fresh 

 urine of a golden sherry tint, and the mouth of each was guarded by a 

 pledget of cotton wool. Two were insolated, one encased. 



Aug. 1. — The contents of the encased tube were turbid and putrid, but 

 the urine in the tubes which were exposed to the light remained perfectly 

 pellucid. One of these (a) was now encased, the other (b) was left as 

 before. 



In about a week two small tufts of mycelium had appeared at the 

 bottom of the tube marked a, the solution in which, however, was other- 

 wise perfectly clear. 



Oct. 13. — The urine in tube b was as clear as when the experiment was 

 first started, nor could any thing except mycelium with sporidia be dis- 

 covered in tube a on close examination with an immersion T y. The 

 urine in this tube had a strongly acid reaction. On the other hand the 

 urine in the tube which was encased from the first was so offensive as to 

 render the examination of even a drop a disagreeable task. It contained 



