392 
Micro-organisms and their Action 
as the digestive organs with every breath of air, and every 
mouthful of food. The possibility is not even excluded of 
micro-organisms entering the orifice of the teat and working 
their way up into the milk cistern during the interval from one 
milking to the next ; but the healthy animal tissue has never 
been found to contain micro-organisms, and animal tissue forms 
the chief material for the formation of milk. During the 
period of lactation there is a constant and very active degener- 
ation of certain cells in the cow's udder going on, the degener- 
ated cells being replaced by new ones, which soon undergo the 
same process of decomposition, the products of which are the 
component parts of milk. The largest portion of the solids in 
milk are derived from this source, while most of the water and 
most probably part of the solids are transudated from the 
blood. 
In accordance with this view of the formation of milk, it 
must be declared impossible that the latter should contain 
micro-organisms when being formed. The only way in which 
they enter the milk is from outside, after it has been drawn 
from the udder. 
This hypothetical view is fully supported by practical 
experience. Lister and other investigators first tried to prove 
whether the ferment which causes lactic fermentation was 
regularly present in absolutely uncontaminated milk. They 
failed in their early experiments to get a milk which would not 
curdle, or decompose in some other way, after it had been kept 
for a time under conditions which effectually prevented germs 
from entering the milk. They succeeded, however, when by 
experience they had learned to avoid all those circumstances 
which could interfere with the experiments and obscure the 
results. Similar experiments, but on a much larger scale, and 
with the practical purpose in view of keeping milk in a pure 
and absolutely unaltered state for some length of time, were 
made by O. Pohl of Liverpool. Pohl's method of preserving 
milk, for which he has taken out a patent, is mainly as 
follows : 
Clean glass bottles, closed with a stopper made of compressed asbestos, are 
placed in a suitable room and annealed in order to completely destroy aU 
organic life. On cooling, the air in the bottles is contracted and sui)plemented 
by air which is filtered by passing through the porous asbestos stopper, and 
thus freed from all impurities, inorganic and organic. When the bottle is to 
be used, the stopper is removed and replaced by a funnel with a bent tube, to 
prevent froth entering the bottle. It is best to heat the funnel before use. 
The milk is then drawn from the udder of the cow du-ectly into the sterilised 
bottle, which is closed with the asbestos stopper as soon as it is filled. 
By thus avoiding the use of other vessels, and assuming that 
proper care is taken that the cows' udders arc quite clean, and 
