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I take a tube of sterile water, and shake up the spores of 
the Mucor thoroughly in it, thus distributing the spores of the 
fungus, and any impurities present, far apart in the liquid. 
I then take a sterile tube of gelatine, rendered nutritious by 
the addition of some vegetable extract and melted by placing 
the tube in water at 25° C., and transfer a few drops of the above 
emulsion of mixed spores to the liquid gelatine medium. <A 
sharp shake up separates spores and impurities even further apart 
than before, and now the contents of the tube are poured on to a 
perfectly sterile glass plate, on which the gelatine rapidly flows in 
a thin film and sets to a firm clear jelly. In this 
jelly there will now be imbedded, at various distances 
apart, the spores of the Mucor and _ those of the 
foreign contaminants from which separation is desired. In 
a few hours—it may be 12, 24, or 48 or more—each isolated spore 
will begin to germinate in its fixed position if the conditions suit 
it, and since we can observe this under a microscope it is not 
difficult to pick out the young mycelium as it develops with a 
sterile needle and transfer it bodily to a new sterile tube of the 
culture medium. 
If the original sowing of contaminated material contained 
many spores, however, it may be that this first “ isolation plate ” 
will still be far too crowded to allow of our picking up only one 
mycelium, therefore I almost invariably proceed as follows :— 
Having shaken the spore material in the distilled water, I have 
ready 6 gelatine tubes, which we may call A, B, C, &c., standing 
in water at 25° C., and 6 plates to be labelled a, 4, ¢c, &c. 1 
then make the first plate (a) as already described, but take care 
to pour into it only about g-1oths of the spore-laden gelatine 
of the tube A. 
The tube A is then filled up with the spore-free gelatine of 
tube B, thus distributing—by shaking—its remaining 1-10th of 
spore-laden gelatine into the newly added gelatine, and again 
g-10ths of this are poured into a second plate (6), where it runs 
and sets as before. Now it is evident that the plate 4 will only con- 
tain about 1-10th as many spores altogether as does the plate a, 
and since these are distributed over an equal area they are more 
widely separated one from another. I then take a third tube of 
spore-free gelatine and add its contents to the tube A, in which 
1-10th of the spore-laden gelatine remains—z.e., about 1-100th 
of the original spores—and repeat the process, and so on to the 
fourth, fifth, and sixth. 
Obviously, then, each successive plate will contain theoretically 
1-10th of the number of spores previously sown : so that if plate a 
has 10,000 spores, 6 will have 1000, ¢ only 100, and @ only 10, 
the fifth (¢) only 1, and the sixth plate (f) none. And in practice 
it is found that a properly made series of plates has fewer and 
