256 Dr. J. M. Hobson’s Notes on Sewage Purification. 
the maximum reached during the previous seven days being 
76° F. After this some rain fell, and the number of organisms 
still further rose on the 16th to 72,000,000. The effluent on the 
same day and at the same hour also showed an increase to 
476,400. It will be noted, however, that the increase of the 
effluent organisms was not at all commensurate with those of 
the sewage. From this date till the end of the month the mean 
temperature remaining high (about 50° F.), and rain falling at 
intervals, the numbers showed still further increase; but I will 
not give them, as the plates were so crowded, and the gelatine 
became so liquid through abundance of organisms known as 
‘‘ liquefiers,” that countings were not reliable. 
I will now advert to the second section of my observations, 
namely, the isolation and separate cultivation of specific orga- 
nisms. Plates as before are used, and gelatine inoculated with a 
small quantity of the material. Individual colonies are selected 
for observation and secondary inoculations made from them. By 
this means pure cultures are obtained, and various media again 
inoculated from these. The behaviour of the growths on the 
various media under lower (20° C.) and higher (87° C.) tempera- 
tures are observed, and microscopic slides made. 
From the sewage I succeeded in isolating twenty species, viz. 
thirteen bacilli, five micrococci, and two sarcinez. I was able to 
diagnose the majority of these, but the rest were unnamed. 
From the effluent I also isolated ten bacilli, two micrococci, 
and two sarcine. One of the micrococci (M. wree) was also 
found in the sewage. It is doubtful if the other micrococcus 
and the sarcine were identical with those found in the sewage. 
The bacilli were all distinct, so far as I could make out. Itisa 
noticeable fact also that whereas most of the organisms of the 
sewage would grow at 37° C., several of those of the effluent 
would not grow at that temperature. 
I found the Bacillus coli communis in the sewage, but did not 
isolate it from the effluent. So far as my observations go, this 
seems important, as sanitarians regard its presence in drinking 
water as evidence of sewage pollution. It would appear as if the 
bacterial flora of the sewage had been stopped and a fresh flora 
from the soil added. Still, my observations are very limited, and 
should be regarded in the light of an initiatory attempt. 
It would be extremely interesting to have a sufficient number 
of observations to be able to trace the effects of heat and rainfall 
upon the bacterial population of the sewers. 
