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poison to such forms as will grow freely on sterilised slices of 
potato, carrot, banana, beet, artichoke, or on agar—a vegetable 
product—mingled with decoctions of plums, grapes, oranges, &c, 
or with beer-wort. 
Passing now to the second case, just referred to, perhaps 
the most difficult of all processes, though it is at the 
same time one of the most valuable and interesting, is that of 
the isolation and germination of spores in hanging drops under 
the microscope. The end to be attained can be reached in 
various ways. Here will be described only the method I generally 
employ, using for illustration a spore of Botrytis, or any other 
which is large enough to be readily seen with a good hand-lens, 
because I want to describe how the ideal hanging-drop culture— 
where the drop contains only a single spore—may be prepared. 
Having obtained a pure culture of Botrytis by separation on 
plates, and transferred it to a tube of some medium on which it 
readily grows and forms conidia—e.g., wort-agar—we have in 
a few days abundant crops of the grey-brown spores. 
A sterile platinum wire easily removes hundreds of such spores 
if passed through the crop, and these are shaken up in a tube of 
gelatine medium—¢e.g., wort-gelatine—and thus disseminated 
through the mass as in the preparation of separation plates. 
On now dipping the point of a needle into the spore-laden 
gelatine,and touching a coverslip with it, a drop is obtained, anda 
glance with the microscope—or, in this case, even a good hand- 
lens—at once tells us whether the drop has brought with it one 
or more spores or not. If each of several trials yields no spore, 
the sowing in the tube was too small, and more spores should 
be added: if the sample drops contain many spores, more 
gelatine is to be added to the tube, until the average drop brings 
out only a few—say 1 to 10—spores. This object achieved, 
we may then proceed as follows : — 
A number of glass culture-cells are to hand, already plugged 
and sterilised in large tubes holding three or four each. One of 
these is laid on a glass slide, hot from the Bunsen flame, and 
cemented to the slide by placing a bit of paraffin of M.P. 60° C. 
at the edge, where it melts and runs in, and solidifies as the 
slide cools, cementing the cell to the latter. 
Meanwhile a number of thin cover-slips are placed between 
plates of talc, and sterilised by the Bunsen flames, and allowed to 
cool. Then sterile water is placed in each arm of the culture- 
cell, and the apparatus is ready. 
Taking one of the sterile cover-slips held by forceps at one 
corner, a minute drop of gelatine from the spore-laden tube is 
placed in its centre, and the cover-slip rapidly inverted and laid 
on the culture-cell, to which it now forms the roof, the gelatine 
drop pendent from its lower side—a “ hanging drop.” 


