Report on the Bacteriology of Water. 391 



In the following plates I have plotted the curves obtained from the 

 means of the foregoing illustrative series of analyses. They bring 

 out very clearly the differences in numbers referred to, and I am 

 strongly of opinion that much valuable information would result 

 from a systematic series of monthly analyses of the Thames water 

 conducted along these lines. 



I by no means pretend that the numbers themselves are of abso- 

 lute value, any more than are those obtained by the ordinary 

 methods of counting averages ; but I do think that the selected cases 

 suggest possible lines of departure for the systematic bacteriological 

 analysis of such a river as the Thames, if a sufficient number of other 

 data were taken in at the same time. These data should include at 

 least the following : (1) the temperature of the river, (2) the amount 

 of sunshine, (3) the organic analysis of the water, (4) the rainfall. 



I am perfectly alive to the incompleteness of the above analyses in 

 these respects, and they are only intended to show what I think 

 should be done by a competent staff of assistants, if any attempt is 

 made at a thorough investigation of the bacteriology of the Thames' 

 and the same applies to any other water. 



The particular object of the above analyses was to test the view 

 that the actual number of bacteria present in winter is less than that 

 in summer, and they strongly confirm that ; and if we remember that 

 this was so in 1893 in spite of (1) the river being lower in August, 

 and therefore more concentrated as a food liquid, (2) the temperature 

 being higher, and therefore more favourable to bacterial growth, it 

 seems at least highly probable that the diminution in the bacteria is 

 largely due to the increased insolation. 



Nor is this all (though I defer the fuller consideration of this 

 point) that my analyses suggest. I find very distinct evidence that 

 the bacteria in the summer water are many of them enfeebled forms, 

 suggesting a distinct inhibition or weakening of their powers of 

 growth. In some cases it is certain that forms obtained in August, 

 and which afterwards turned out to be identical with forms found in 

 the winter, at first grew so feebly that their characters on the plates 

 led one to put them down as distinct species or varieties. 



I have given some experimental evidence bearing on this, and 

 going to prove that it is due to the action of light on these forms. 

 The matter is a very complex one, and I must refrain from further 

 discussion of it until all the forms isolated during the year are worked 

 out ; but it is worth while, I think, to draw the attention of investi- 

 gators to the matter. In one or two cases, at least, there is no 

 question that exposure to light does so affect the germination and 

 growth of the bacteria, that the resulting colonies depart widely 

 from the normal in many of their characters. 



I have in hand a large number of experimental results obtained 



