AND ITS BEARINGS ON PATHOLOGY 373 
On the 30th of August last, having provided sixteen pure glasses of boiled 
milk, and having estimated, in the manner already described, the number of 
bacteria present in every I-50th minim of a glass of boiled milk which had 
been inoculated the day before by touching it with a heated needle dipped in 
milk curdled under the influence of the pure ferment, I diluted a drop of this 
milk with boiled water to the requisite degree, and introduced into each of 
ten of the sixteen uncontaminated glasses a drop calculated to contain on the 
average a single bacterium, while five of the rest received each a drop supposed 
to contain two of the organisms, and the remaining glass was inoculated with 
a quantity in which, according to the estimate, there would be four bacteria. 
The result was that within three and a half days the glass into which four 
bacteria were supposed to have been introduced contained a curdled mass, 
and the five which had received the drops arranged for two bacteria each had 
all undergone a similar change. Of the ten inoculated with drops averaging 
one bacterium each, the majority were at this period still fluid ; but some assumed 
the solid condition in the course of the next twenty-four hours, though at 
different times. But of this series of ten exactly five, as it so happened, remained 
permanently fluid. 
This was just the sort of occurrence which might have been anticipated 
if we believed the bacteria to be really the cause of the fermentative change, 
and supposed that we had succeeded in forming a fair estimate of their numbers. 
It was to be expected that the bacteria would not be distributed with perfect 
uniformity in the water with which the milk was diluted; and hence, of the 
drops containing on the average one bacterium each, some would probably be 
destitute of the organisms, and the rest have more than one, and in differing 
numbers, involving slight differences of time in arriving at the stage of the 
fermentative process which induced coagulation. 
But not only were the results of this experiment in harmony with the view 
that the Bacterium lactis was the real fermentative agent: they would, as 
I believed, afford indisputable evidence of the truth of the theory, provided it 
should turn out, as former experience made me feel sure would be the case, 
that every glass which had curdled contained the bacterium, and that every 
one which remained fluid contained none. Though, as I have said, I did not 
doubt that this was the state of the case, yet I went through the laborious process 
of examining the contents of all the sixteen glasses just before leaving Edin- 
burgh, nine days after the time of the inoculation. All those which had coagu- 
lated still contained an unaltered white curd with a glistening upper surface, 
and nothing to indicate the supervention of any change secondary to that of 
the lactic fermentation. The air in the glass shade of each had the odour of 
