18 BACTERIOLOGICAL DIAGNOSIS. 
grammes of gelatin for each 100 c.c.; allow to soak 
for an hour or more, and then heat until the gelatin is 
dissolved. Continue the heat and render the medium 
faintly alkaline just as was done in the preparation of 
broth. Now filter through a moistened filter paper. 
To avoid the setting of the gelatin during the filtration 
it is best to use a double jacketted funnel containing hot 
water, but if this is not at hand the whole apparatus 
(flask and funnel) may be placed in the steam steriliser 
(the lid being kept off to avoid the drops of condensed 
water which might otherwise fall into the funnel) or in 
a waym (but not hot) oven and left at a temperature of 
about 40° C. until the process is complete. 
The gelatin which is made by the above process is 
sufficiently clear for most purposes. A more sightly 
medium may be-made by clarification of the above by 
white of egg. To the medium (after neutralisation but 
before filtration) add the white of one egg for each 250 
or 300 c.c. of fluid and shake thoroughly. Now boil in 
the steamer for half an hour and filter as before. 
Test-tubes are filled with gelatin just in the same 
‘way as with broth, and the process must be carried out 
quickly to avoid solidification of the medium. Some 
of the test-tubes are allowed to cool in the vertical 
position, others lying in a sloping position so that the 
upper surface of the gelatin forms an ellipse some three 
inches long. The former tubes are inoculated by 
driving a straight platinum needle charged with the 
material containing the bacteria into the gelatin in the 
axis of the tube; cultures made in this way are called 
“stab-cultures.” The gelatin ‘“‘slopes” are inoculated 
by drawing the charged needle along the surface of the 
medium, care being taken not to plough it up; cultures 
made in this way are called “ stroke-cultures.” 
