68 



Dr. Edivard Franhland 



[Feb. 21, 



ascertained, however, that the Thames basin had been [twice very 

 thoroughly washed out by heavy floods shortly before the time when 

 the November sample was taken, and this affords a satisfactory ex- 

 planation of the anomalous result yielded by this sample. 



These comparisons therefore demonstrate that the number of 

 microbes in Thames water depends directly upon the rate of 

 flow of the river, or, in other words, on the rainfall, and but 

 slightly, if at all, upon either the presence or absence of sunshine 



Fig. 15. 



or a high or low temperature; and they are confirmed by' the con- 

 tinuation of these observations during the year 1895. (See diagram, 

 Fig. 16.) 



With regard to the eff'ect of sunshine upon bacterial life, the 

 interesting observations of Dr. Marshall "Ward leave no doubt that 

 sunlight is a powerful germicide ; still, it is obvious that its potency 

 in this respect must be greatly dimini sbed, if not entirely annulled, 

 when the solar rays have passed throu gh a stratum of water, of even 



