72 ESSENTIALS OF BACTERIOLOGY 



water for half-hour or digest in autoclave fifteen minutes. 

 Restore loss by evaporation and allow to cool to 60 c.c. 

 To meat-water infusion (500 parts meat to 500 c.c. 

 water) add 2 per cent, peptone, also 500 c.c. agar solu- 

 tion. Titrate after boiling one minute, and adjust 

 reaction to -f-i. Heat in steam-bath forty minutes, and 

 proceed as with nutrient gelatin, i. e., restore loss, read- 

 just reaction, and filter and refilter until clear. The 

 filtering should be done while the solution is hot. Pour 

 into tubes or plates, sterilize in au- 

 toclave, and finally slant the tubes 

 so as to obtain a larger surface. 

 (Most agar tubes are used for stroke 

 cultures.) 



The addition of the white of an egg 

 will often clear it up; if this avails 

 not, refiltering several times and at- 

 tention to the few points mentioned 

 will produce a clear solution. 

 Lactose Litmus Agar. One per cent, 

 lactose added to nutrient agar just 

 before sterilization. Reaction neu- 

 tral. One per cent, azolitmin 

 (Kahlbaum) boiled five minutes and 



added either to the tube ^fore final 

 sterilization or, if media usod in 



plates, added at the time of plating. 



Preparation of Nutrient Blood-serum. If the slaughter 

 of the animal can be supervised, it were best to have the site 

 of the wound and the knife sterilized, and sterile flasks (Fig. 

 20) at hand to receive the blood directly as it flows. 



The blood is placed on ice forty-eight hours, and the 

 serum is drawn out with sterile pipets into test-tubes, avoid- 

 ing shaking of the jar. These are placed obliquely in an 

 oven where the temperature can be controlled and main- 

 tained. (See Fig. 21.) 



Coagulation of Blood-serum. The tubes of blood-serum 



