54 PRACTICAL BACTERIOLOGY 



4. Place in the steam sterilizer one to two hours. 



5. Filter through ordinary filter paper or flannel in the steam 

 sterilizer.* 



6. Fill the desired quantity into test-tubes, and close with cotton 

 wadding plugs. 



7. Sterilize in the steam sterilizer for fifteen minutes on each of 

 three successive days. 



XCIV. GRAPE SUGAR AGAR. 



Add half a gramme of grape sugar to 100 c.c. of agar-agar medium 

 after it is filtered, and proceed as at 93, No. 6. In filtering grape 

 sugar agar into tubes it is customary to fill the tubes two-thirds 

 full, as this medium is used in the investigation of anaerobic and 

 gas-forming bacteria. 



XCV. GLYCERINE AGAR. 



Add 4 to 6 grammes of glycerine to 100 c.c. of agar-agar medium, 

 either before or after filtering, and proceed as at 93, No. 6. 



XCVI. WURTZ'S LACTOSE LITMUS AGAR. 



1. To ordinary slightly alkaline agar-agar add 2 to 3 per cent, of 

 lactose. 



2. Fill into tubes and sterilize by the ordinary method for three 

 consecutive days. 



3. When sterilization is complete, add enough sterilized litmus 

 tincture to give the medium a decided pale blue colour. 



Bacteria causing fermentation of lactose, when grown on this 

 medium, develop into colonies of a pale pink colour with a corre- 

 sponding reddening of the surrounding medium. Bacteria incapable 

 of producing fermentation grow in pale blue colours and cause no 

 reddening of the surrounding media. (Instead of agar-agar, ordinary 

 nutrient gelatine can be substituted in the preparation of this medium.) 



XCVII. BLOOD AGAR. 



1. A few drops of human or pigeon's blood, obtained under sterile 

 precautions, are spread over the oblique surface of some ordinary 

 sterile agar-agar tubes. 



* The author filters agar through two pieces of moleskin cloth under pressure. 



