92 BACTERIOLOGICAL ANALYSIS LESSONS i, n 



To prevent the agar-agar from slipping, after having 

 been slanted, allow it to cool and set slowly, and 

 keep the tubes for one or two days at the tempera- 

 ture of the room. 1 



XIII BLOOD SERUM (LORRAIN SMITH'S METHOD). 



(1) To prepare sloped serum tubes, take 100 cc. of fresh 

 ox serum, collected under aseptic precautions. 



(2) Add to it 1 to 1*5 cc. of a 10 per cent solution of 

 caustic soda and shake it gently. 



(3) Pour the serum into test-tubes and sterilise them, 

 in a sloped position, in the autoclave at 120 C. for twenty 

 minutes, or in the steamer on three successive days. 



By this method almost transparent serum may be 

 readily obtained. 



Serum tubes are of especial value in the cultivation 

 of diphtheria bacilli, for diagnostic purposes, and 

 also in the separation of tubercle bacilli. 



1 In preparing agar-agar according to the above method it is not 

 necessary to clear with the white of an egg, though this considerably 

 improves the clearness of the medium. To hasten nitration, in case 

 this should be slow, as occasionally happens, instead of changing the 

 papers the hot agar-agar may be first passed through Papier Chardin 

 (Cogit and Co., Paris), and then through two layers of Swedish filter- 

 paper. In any case, before filtering, the agar-agar should be heated up 

 properly. 



