34 MICRO-ORGANISMS AND DISEASE [chap. 



peptone, and salt to 600 ccm. of the broth ; further process 

 is as above. 



It is this gelatine which I generally use as " nutrient 

 gelatine," not Koch's meat infusion gelatine, for I find that 

 beef decoction gelatine as prepared above is conspicuously 

 a better nutritive medium than the meat infusion gelatine 

 prepared after Koch's method. 



3. If it is necessary to expose the cultivation to higher 

 temperatures than 25° C, the nutrient gelatine cannot be 

 used as a solid medium. Solidified blood serum, or sohdi- 

 fied hydrocele fluid, or solidified ascites fluid, or solid 

 Agar-Agar mixture (Koch) must then be employed. 



The first — i.e. the serum of blood, the hydrocele fluid, 

 and ascites fluid — can be made solid by heating them in 

 tubes (see page 51) gradually up to 68°, 70°, or 71° C. 

 When this temperature is reached the material soon turns 

 solid, losing slightly its limpidity, but when solidified with 

 slanting surface (see serum inspissator) is sufificiently trans- 

 parent for all practical purposes. By heating it rapidly, or 

 heating it above 72°, it becomes sohd, granular, and opaque. 

 Of course, once thus made sohd it cannot be liquefied 

 again, and therefore must be already contained in the 

 vessels (test-tubes and small flasks) in which the growth of 

 orga.nisms is to be carried on. 



4. Lofflers serum, very useful for cultivation of the 

 diphtheria bacillus on which this microbe grows with pre- 

 dilection, is composed of two parts of blood serum and 

 one part of faintly alkaline beef broth ; the fluid contained 

 in sterile plugged test-tubes is sterilised and solidified with 

 slanting surface in serum inspissator just like ordinary blood 

 serum. 



Serum solidified with slanting surface always shows on 

 cooling a small amount of " condensation water''; but this 



