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fewer spores, more and more isolated after each dilution, in pro- 
portions sufficiently like this to make the illustration applicable.* 
Of course, experienced hands and eyes soon learn to appreciate 
the relative sizes and numbers of the spores and impurities to be 
dealt with in the first instance. If one has a good, clean 
growth of the Mucor to begin with, with up-standing sporangia 
yielding plenty of clean spores to a touch of a moist needle point, 
hardly any trouble will be met with, and the second or third 
plate will probably yield perfectly pure and well isolated mycelia; 
but if the original spore material is derived from a rotting fruit, 
or macerated tissues, for instance, there may be far more bacteria, 
infusoria, and moulds, &c., than Mucor spores, and it may result 
that even the sixth plate was not sufficiently dilute, and other 
series have to be made with the partially purified material, until 
perfect isolation is at last assured. 
Troublesome and tedious though this method may at first 
sight appear, I have found that it is the shortest in the end 
wherever it is seen at the outset that the fungus desired will 
grow on such a medium as the gelatine referred to. This is 
by no means always the case, however, and even such substitutes 
for gelatine as agar, apple-jelly, quince-mucilage, &c.—all of which 
I have used with more or less success in special cases, as well as 
the curious mineral silica jelly, so difficult to prepare and use 
successfully—fail with many fungi. It would take us too far to 
discuss the special methods which may be employed for isolation 
in such cases, as well as to enumerate the many fungi which have 
hitherto resisted all attempts of the kind. 
It may surprise some of you to learn that Saprolegnia—its 
name refers to its habitat in putrid substances, swarming with 
bacteria and infusion—can be isolated and grown in pure culture 
on artificially prepared media, yet such is the fact. If we place 
a small tuft of actively growing Sapro/egnia at a time when the 
zoosporangia are just emitting their zoospores, in water 
sterilised by a Pasteur filter and in which a few sterilised flies 
have been cast, a few hours suffice for infection and the develop- 
ment of nearly bacteria-free growths from which re-infection on 
sterilised flies’ legs can easily be got. 
On placing such'a preparation on the sloped surface of gelatine 
prepared with extract of meat—of course properly sterilised—the 
fungus rapidly grows out in a radiating fringe round the fly’s leg, 
and from the outer edges of this halo-like fringe pieces can be 
obtained almost devoid of bacteria. Such a piece, transferred 
to another tube, gives a still cleaner culture, and by repeated 
transferences to new tubes, pure cultures are at length obtained. 
Or boiled peas can be employed instead of the gelatine, as Klebs 
has shown. 
* The method is a particular modification of a procedure known generally 
in all bacteriological and botanical laboratories, 
