564 
PIERRE A. FISH. 
“ The Drop Method (Wynter Blyth).—Sterilized distilled 
water is infected with the test organism, and measured volumes 
of the infected water are added to known volumes of the anti¬ 
septic. After a given time a drop of the mixture is added to 
io to 20 grammes of liquefied gelatin medium, and the growth 
watched. Bouillon is a more suitable medium, as many patho¬ 
genic germs grow slowly at temperatures at which gelatin re¬ 
mains solid and retains its distinctive advantages. Bouillon 
has also been shown in Miquel’s experiments to give greater 
opportunity for the growth of organisms whose vitality has been 
reduced than the solid media. If it is desired to use micro¬ 
organisms from cultures in solid media, the growth is scraped 
off with a wire and suspended in sterile distilled water. Such 
suspensions, filtered to remove flocculi, are employed advan¬ 
tageously, because the disturbing effects of varying media and 
the presence of precipitates are avoided. 
u The Thread Method. — This is often known as Koch’s 
method, as it was employed by him in examining the action 
of antiseptics on the spores of bacillus anthracis. Sterilized silk 
threads were soaked in cultures containing anthrax spores (or, 
better, suspensions of spores in sterile water) and dried. The 
threads were allowed to hang in the antiseptic for the desired 
time and afterwards withdrawn, washed in sterile water, and 
inoculated either into animals or fresh nutrient media. Koch 
employed solid media for his inoculations. This method has 
been much used, and possesses the advantage that the antiseptic 
can be got rid of by washing. If fluid media are employed for 
the test cultures it possesses also the advantages of the dilution 
methods. When employed for non-spore bearing organisms the 
intermediate drying should be omitted, as that itself will diminish 
the vitality of many organisms in the vegetable form. Suspen¬ 
sions in sterile water are preferable to fluid cultures in which to 
soak the threads, as the (often albuminoid) medium forms a 
coating when dry which protects the organisms. In all cases 
control experiments must be made in which threads are treated, 
just as are the test threads except that sterile water is substituted 
