IN THE TROPICS. 
35 
spherical bulb, which is filled with wadding. The other tube 
(b) is drawn out to a point and covered by a protecting 
tube (c). The jet must be so fine, that when used it shall 
only give one or two drops ; fungus cultures being usually 
made on the slide in a drop of nutrient solution, the flask 
must not furnish too great a quantity. In order to keep out 
particles of dust the protecting tube (c) is closed with a plug 
of wadding damped with alcohol. The wadding in the blow- 
tube (a) is sterilized with corrosive sublimate before being 
used. Wadding is an excellent bacterium filter in Europe 
without further treatment, but in the tropics, where the air 
is so damp, especially in the wet season, mould fungi are 
easily able to get through it ; in a few days the ubiquitous 
spores begin to germinate and send their hyphæ through 
the thick tissue of the wadding, and in a very short time 
the under side is quite green with the plentifully formed 
conidia of Pénicillium. Against this danger the sublimate 
is a protection. The cork or rubber stopper of the flask 
must be protected in the same way against the entrance of 
spores or hyphæ. If these precautions are carefully attended 
to, the flask may be used for years without any fear of con- 
tamination. 
It is obvious that the nutritive solution should be steri- 
lized only after it has been introduced into the flask, and 
that the wadding in the b'ow-tube (a) should not be inserted 
till after this has been done, otherwise the steam will carry 
particles of the corrosive sublimate into the solution. The 
cork of the flask (d) may be fastened down with a thread to 
keep it permanently in one position, and the flask should 
never be opened without real necessity, and for a short time 
only. In this case care should be taken to hold the flask 
erect, to hinder the entrance of the countless spores of the 
tropical air. A fresh sterilization is to be recommended after- 
even a single opening. It is also necessary to examine the 
fluid microscopically from time to time to make sure that it 
is completely sterile and contains at most only dead germs. 
( 6 ) 
