AND ITS BEARINGS ON PATHOLOGY 383 
organisms as real, as distinct in structure, and as potent in their effects, as is 
the Bacterium lactis. 
But while we have thus reason to think it not unlikely that ultra-micro- 
scopic fermentative organisms may exist, we have no grounds whatever for 
believing that bacteria visible under the microscope have ultra-microscopic 
germs. The sole reason for the frequently expressed opinion, I may almost 
say axiomatic assumption, to that effect is, I believe, the fact that while ordinary 
water has been shown to cause the development of bacteria when introduced 
into organic liquids even in small quantity, yet no bacteria can be discovered 
in it by aid of the microscope. But we are apt to forget how extremely difficult 
it is, with the very high magnifying powers which it is needful to use, to discover 
such minute objects as bacteria unless they are present in large numbers. Now, 
if we recall the experiments above related of inoculating milk with very minute 
drops of water,’ we see that in the sample of ordinary tap-water examined there 
could not be more than about one particle capable of producing a bacterium 
in every I-100th minim. A drop of that size, small as it is, would, if placed 
between two flat plates of glass for microscopic examination, spread itself over 
a space about half a square inch in area, and we might search such a drop for 
an entire day without finding an individual bacterium contained in it. I once 
took the trouble to try whether I could find the Bacterrum lactis in some milk 
diluted with boiled water to the degree requisite to produce on the average 
one full-sized individual to every hundredth of a minim, but failed to do so 
with a protracted search. But the difficulty would have been immeasurably 
increased if the bacterium had resided for three days in the water and had 
acquired the characters represented in Plate XIV, Fig. 11, so minute and in- 
definite that an individual, if placed fairly in the field of the microscope, would 
probably not attract attention at all, or if it did so, would be passed over as of 
uncertain nature. In this connexion I may mention a hitherto unpublished 
observation which I made five years ago. I introduced some tap-water into 
three capped liqueur-glasses, purified by heat, and placed under glass shades. 
After a week had elapsed, on taking the glasses into a dark room and examining 
the water, with a candle placed on the other side of the vessel (a very good way 
of detecting the first appearances of nebulosity produced in a transparent fluid 
by bacteric development), I could just discern upon the free surface a delicate 
bluish film, which, on microscopic examination, proved to be composed of 
closely packed motionless bacteria of various forms, and for the most part of 
extreme minuteness. This explained an appearance which had before puzzled 
me, viz. that when water had been left undisturbed in a wine-glass for a day 
Wrelle [Sy sto 
