l8 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 warm (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." 



