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interfere with the homogeneity of the liquid. In so far as 
relates to the ultra-microscopical origin of the bacteria, this 
inference harmonises entirely with what has been stated 
above as to their development in gelatinous masses from foci. 
Here, as in the other case, it would surely be an error to 
suppose that in these proliferous foci the apparently hyaline 
material is really homogeneous. It appears to be so, merely 
because the particles are so extremely minute. Hence when 
we apply the term matrix to this subject, we must guard 
against the word being understood to imply that in the 
present instance bacteria arise out of an amorphous jelly. 
What is meant is, that the jelly is itself so organised through- 
out, that the smallest conceivable bit of it, if separated from 
the rest, would still possess structure, and consequently the 
power of reproduction. 
Chemical composition of Microzymes, and their relation to 
the media in which they grow.—Of the chemical composition 
of microzymes we know very little. It is assumed that the 
particles are albuminous, because they are readily stained 
with carmine and browned by iodine; but of the matrix little 
can be said, excepting that it is probably also albuminous. 
Chemistry can as yet give no account of the difference 
betweeen them. As regards their action on the liquids in 
which they live the most important facts are: (1) That their 
growth is attended with absorption of oxygen and discharge 
of carbonic acid. (2) That they are remarkably independent 
of the chemical constitution of the medium, provided that 
they are supplied with oxygen; and (8) That they take 
nitrogen from almost any source which contains it, and use 
it for the building up their own protoplasm. 
It is this last power which specially indicates what may be 
called their place in nature as the universal destroyers of 
nitrogenous substances, acting as the pioneers if not the pro- 
ducers of putrefaction. They exercise this function not by 
virtue of any special relation of their own nutritive processes 
to putrefaction as such, but simply by their extraordiuary 
power of seizing on the elements which they require for the 
construction of their own bodies. 
The necessity of oxygen to bacteria is so great that they 
cannot grow even for a short time without it. Thus if liquid 
containing living bacteria be placed under a cover glass for 
microscopical examination, it is seen that towards the centre 
of the cover glass their movements become sluggish and 
eventually cease, although towards the edges they are still 
lively. If bacteria are confined in a tube without air they 
soon die. If the supply of air is limited they continue to 
