Report on the Bacteriology of Water. 419 



far more favourable, there can be no reasonable doubt that they did 

 not undergo any increase but only decline ; this supposition is, more- 

 over, corroborated by the results of the examinations by phenol 

 broth-culture, to which I shall presently refer. 



I will now turn to the similar examinations made by gelatine plate- 

 culture of the same unsterilised Thames water infected with the 

 B. coli communis, the results of which are recorded in the table on 

 p. 418. 



The results recorded in the above table for the B. coli communis are 

 almost precisely parallel to those recorded in the previous table for 

 the typhoid bacillus. There is again, in the case of the water kept at 

 the winter temperature of 6 8 C., the enormous multiplication in 

 the total number of bacteria present, followed by rapid and almost 

 continuous subsequent decline. In the case of the water kept at the 

 summer temperature of 19 C., a slight increase was observed on the 

 occasion of the second examination (but, as pointed out in the case of 

 the typhoid table, a great increase followed by rapid decline may have 

 taken place in the interval between the first and second examina- 

 tions), after which there was a great decline followed by some re- 

 crudescence at the end. In the case of the waters kept both at the 

 winter and the summer temperatures respectively, however, it is 

 obvious that extensive multiplication of the water-bacteria must have 

 taken place, owing to the very large increase in the number of 

 colonies causing liquefaction of the gelatine which was observed. 



For the same reasons as stated in the case of the typhoid bacillus 

 (see p. 417), it is impossible to form any estimate of the numbers in 

 which the coli bacilli were present after the day (11.5.1893) of their 

 introduction, nor as to the length of time over which they persisted in 

 the living state in these waters. From the corresponding experi- 

 ments, however, made with the steam-sterilised Thames water, it is 

 quite possible that the B. coli communis, unlike the typhoid bacillus, 

 may have undergone some multiplication in the water. It is to the 

 examinations by the method of phenol broth-culture that we must 

 again have recourse in order to ascertain how long the coli bacilli 

 remained alive in these unsterilised waters. 



There is a point which is brought out very strikingly in these 

 tables, and to which I would draw attention at this stage, and that is 

 that the total number of bacteria present in these unsterilised waters 

 at the end of the period over which these experiments extended, was, 

 both in the case of the uninfected waters (see table, p. 413) as well as in 

 that of the typhoid (see table, p. 415), and in that of the coli (see table, 

 p. 418), greater in the water maintained at the summer than at the 

 winter temperature respectively. The probable explanation of this 

 phenomenon would appear to be that at the lower temperature 

 (6 8 C.) many of the bacteria present may be unable to form spores, 



