II.] PREPARATION OF CULTURE MATERIAL. 23 



add to this 60 grams of the finest gold label gelatine cut up 

 in small pieces, 6 grams of peptone and 6 grams of common 

 salt. Dissolve on waterbath, but do not let the water boil ; 

 neutralise with carbonate of soda or, better, liquor potassae 

 till faintly alkaline ; boil for half an hour, filter by hot filter, 

 (see Fig. 6) into a sterile flask plugged with sterile cotton-wool, 

 and bring it up to boiling point, at which it is kept for a few 

 minutes. This can be kept as stock gelatine, or can be 

 decanted at once into sterile test-tubes plugged with sterile 

 cotton-wool. Keeps solid up to about 25 C. 



Prepared in this manner the nutrient gelatine passes easily 

 and comparatively rapidly through filter paper on hot-filter. 



The same 10 per cent, nutrient gelatine can be of course 

 obtained if broth is already made, e.g. broth in a stock 

 flask, by adding the above-named quantities of gelatine 

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

 is .as above. 



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. Solid blood serum or solid hydrocele 

 fluid (Makins) or solid Agar-Agar mixture (Koch) must then 

 be employed. 



The first, i.e. the serum of blood, and the second, i.e. the 

 hydrocele fluid, can be made solid by heating the above sterile 

 serum or hydrocele fluid in tubes (see page 20) gradually 

 up to 68 or 70 C. When this temperature is reached 

 the material soon turns solid, losing slightly its limpidity, 

 but is sufficiently transparent for all practical purposes. By 

 heating it rapidly, or heating it above 72, it becomes solid, 

 granular, and opaque. Of course, once thus made solid it 

 cannot be liquefied again, and therefore must be already 

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

 the growth of organisms is to be carried on. Or blood serum 



