AND ITS BEARINGS ON PATHOLOGY a7 
And now let me dwell for a few minutes on the inference to be drawn from 
these facts. We have seen that boiled water rendered infective by the admixture 
of a small quantity of milk undergoing the lactic fermentation, having been 
introduced in drops of equal size into ten glasses of pure boiled milk, five of those 
glasses underwent the lactic fermentation, characterized by souring and curdling, 
while five remained altogether unaffected. This proves that the same truth 
holds regarding the lactic ferment which we have before established with respect 
to the various ferments that occur in ordinary water, viz. that it is not a material 
soluble in water, but consists of insoluble particles. For had it been dissolved 
in the water of inoculation, every equal-sized inoculating drop would have 
produced the same fermentative effect. Next we have to consider the bearing 
of our facts on the nature of those insoluble particles, the question being whether 
they were the bacteria or consisted of some so-called chemical ferment destitute 
of life, of which the bacteria were a mere accidental concomitant. Let us 
assume, for the sake of argument, that it is possible for insoluble particles to 
exist devoid of vitality, yet capable of multiplying lke the bacteria. Such 
a notion is unsupported, I believe, by a tittle of scientific evidence ; but, for 
the sake of argument, let us fora moment assume it. We should then be further 
obliged to suppose, in order to account for our facts, that these hypothetical 
particles, though merely accidental accompaniments of the bacteria, were 
present in precisely the same numbers, a thing which is utterly inconceivable. 
But we should have to go further and suppose, what is equally inconceivable, 
that these bodies of different natures, though mere accidental concomitants 
were not only exactly equally numerous, but invariably accompanied each 
other in pairs ; so that when a bacterium was introduced into one of the glasses, 
it was always associated with a particle of the hypothetical true ferment, and 
whenever the bacterium was excluded, the hypothetical ferment likewise failed 
to enter. Hence, as the only other possible interpretation of our facts involves 
what is utterly inconceivable, I venture to think that those facts will be admitted 
calculation, besides leaving uncertainty as to the estimate, in consequence of the development that is 
proceeding in the milk in the glass. But these difficulties are entirely got over by adding a minim of 
the milk to ten minims of boiled water in a purified glass, and using this first dilution both for the estima- 
tion of the bacteria and for furnishing the drop to be diluted for the purpose of inoculation. The milk 
having been well mixed with the water, the bacteria are pretty equally distributed through it, while 
the addition of so much water to the milk greatly retards the development of the bacteria and makes 
hurry unnecessary. Thus, I ascertained in one instance that the rate of increase in some milk so diluted 
and still kept protected in a pure glass appeared to have been only such as to treble the number ot 
bacteria in sixteen hours, whereas they would probably have been multiplied fourfold in two hours 
if the milk had remained undiluted. The dilution has the further advantage that it does away entirely 
with the difficulty caused by the milk globules and molecules in the recognition of the bacteria in un- 
diluted milk, even when in very thin layer. In counting the bacteria I found it convenient to take 
all the fields in succession both in the horizontal and in the vertical diameter of the covering glass, which 
with my microscope gave about a hundred fields from which to estimate the average. 
