180 
president’s address. 
Aug., 1889. 
disappear. A litre of rain water may contain 248,000 
microbes; a litre of water from the Seine, at Bercy, has been 
shown to contain 4,800,000, and at Asnieres 12,800,000 ; 
while water of impurer character showed the enormous total 
of 80,000,000 per litre. These numbers may, perhaps, be 
better comprehended if I say that they vary from 30,000 in 
a pint of brook water to 50,000,000 in a pint of the liquid 
which is called the Thames at London. Even ice contains 
many, especially if “ bubbly” ; the water derived from melted 
hailstones is often thronged. Prolonged freezing is no doubt 
fatal to the majority, but a temperature many degrees below 
freezing point is required to kill them all. 
Of course, if the earth on which we grow our food, the air 
we breathe, and the water we drink are thus permeated by 
these countless numbers of microbes, it must needs follow 
that the human alimentary canal is full of them. They 
abound in the mouth, especially clustering round the teeth, 
and it is a remarkable fact that we can assert without a 
doubt that the species of Leptothrix, which is peculiar to this 
latter habitat, has always existed there ; for Zopf and Miller 
discovered, isolated, mounted, and even stained,the Leptothrix 
from the teeth of Egyptian mummies. Nor is this antiquity 
all that can be proved of Bacteria. Far, far before this, in 
the dim light of carboniferous forests, Bacillus Amylobacter 
rioted in the decaying cells of plants as it does at the present 
day, and has left its traces behind in fossil leaves and stems, 
recognisable even after the lapse of so many ages by the exact 
similarity of its action to that which we now observe. 
In the stomach, and especially in the intestines, the 
number of Bacteria enormously increases, and is greatest in 
the large intestine. It is not improbable that they play an 
important part in the digestion and assimilation of our food; 
this is certainlv their function in the stomachs of herbivorous 
4/ 
animals. But in the blood and in the healthy tissues of the 
body it is probable (according to the evidence of the best 
experimenters) that they are entirely absent. Those observers 
who think they have discovered signs of their presence there 
may have been misled by faulty methods of experiment, 
although it must not be forgotten that the presence of micro¬ 
parasites (not belonging, however, to the Bacteria) in the 
blood of healthy rats is an admitted fact. In any case, if any 
microbes are present in such places, they are only occasional 
intruders. 
But this suggests the question—how are they kept out ? 
The particles of chyle which are absorbed by the walls of the 
intestine are much larger than the Bacteria, and there is, 
therefore, so far, no reason why they should not be absorbed, 
