412 Profs. Percy Frankland and Marshall Ward. 



total number of micro-organisms present, but without any hope of 

 counting or even identifying the typhoid or coli colonies, as this is, 

 for the reasons already given (see pp. 406, 407) in general, quite out 

 of the question. 



On the other hand, the presence or absence of living typhoid and 

 coli bacilli was periodically determined by cultivation with phenol- 

 broth (see p. 407), a method which, of course, does not permit of an 

 estimation of their number, but which, as will be seen, is often able 

 to throw light on their relative abundance or on their relative degree 

 of vitality. 



2. The sterile (porcelain-filtered and steamed) infected Thames 

 waters were periodically examined both by plate cultivation and by 

 the phenol-broth method : so that in the case of these waters, in 

 which the typhoid or coli bacilli were not mixed with other bacterial 

 forms, not only could their presence or absence in the living state be 

 determined, but their actual numbers ascertained. 



3. The unfiltered uninfected Thames water was periodically ex- 

 amined by plate cultivation in order to follow the increase or decrease 

 in the numbers of the water bacteria, whilst examinations by the 

 phenol-broth method were also made in order to ascertain whether 

 there were any forms amongst the water bacteria which might be 

 confounded with the typhoid or coli bacilli, and thus to check the 

 diagnoses made in the case of the unsterilised infected waters. 



1. Bacteriological Examination of the Uninfected Unsterilised Thames 

 Water. (First Series.) 



It will be most convenient to consider first the behaviour of the 

 control waters which were placed under the same conditions, in the 

 incubator and refrigerator, as the infected ones. 



The results of the gelatine plate cultivations of these control waters 

 are summarised in the following table : 



