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. SERUM AGAR-AGAR. 



(1) Take 100 cc. of fresh ascitic or pleuritic fluid. 



(2) Add 2 to 2-5 cc. of a 10 per cent solution of caustic 

 soda, shake gently and heat in the steamer for an hour. 



(3) Now add 1*5 grammes of agar-agar, treated as 

 described on p. 90. 



(4) Heat in the autoclave for about two hours, filter and 

 fill tubes in the ordinary manner. 



Serum agar-agar tubes are of value in the cultivation 

 and separation of diphtheria bacilli, for diagnostic 

 purposes. 2 



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. 



2 The addition of 5 per cent glycerine and 1 per cent grape-sugar is 

 advisable. 



