Lee  — ee 
—— 
NOTES ON MICRO-ORGANISMS. 29 
cultivating, the next thing is to provide a suitable food and keep 
out air-borne germs. Amongst the various cultivating media 
there is nothing much better for Bacteria than plain gelatine, 
which can be adapted for use in a variety of ways; the addition 
of peptone or meat extracts such as Liebig’s and Brandt’s un- 
doubtedly increases the nutrient power. I have found the much 
vaunted Agar-Agar very difficult to deal with ; it is more especially 
suited for disease organisms, but requires the greatest care to 
obtain clear, and with anything like prolonged heating loses its 
power of congealing. ; 
Time will not permit me to enter into the minutiz of sterilising 
vessels, infusions, apparatus, etc. In all cases it is a matter of 
employing heat in such a way as to kill germs that are not wanted. 
Where something short of absolute sterilisation will do, I have 
found glycerine very useful for smearing over the inside of bell- 
jars, the edges of plates, etc., for it holds any dust falling on it, 
and can easily be washed off when desired. In designing a room 
for Bacterial investigation, it appears to me that much might be 
done with tile walls kept moist with glycerine, floors that would 
not make or store up dust, etc. ; in fact, as far as possible, a dust 
free room, for it would save a large amount of trouble from 
accidental inoculation. Every time a room is swept the conditions 
are rendered about as unfavourable for pure cultures as they well 
can be. 
A supply of wide-mouthed bottles, test tubes, and flasks for 
stock gelatine, with a few small pieces of apparatus, will enable 
one to grow ordinary micro-organisms. Such things as water 
baths, drying ovens, etc., can be easily contrived out of every-day 
appliances. 
I have found petroleum to be a very effectual seal against air 
germs in cultivations in gelatine carried out in bottles. The 
petroleum is run on when the gelatine is cold and set. 
There are several methods of obtaining a pure cultivation of 
one particular organism, and, speaking generally, they depend on 
the excessive dilution of a liquid containing a preponderating 
quantity of the organism sought. Such dilution may be carried 
