90 BACTERIOLOGY. 



restored. At the end of the time given remove the flame 

 and place the vessel containing the mixture in a large 

 dish of cold water; stir the agar-agar continuously until 

 it has cooled down to about 68°-70° C, and then add 

 the white of one egg which has been beaten up in about 

 50 c.c. of water; or the ordinary dried albumin of com- 

 merce may be dissolved in cold water in the proportion 

 of about 10 per cent., and used; the results are equally 

 as good as when eggs are employed. Mix this care- 

 fully throughout the agar-agar, and allow the mass to 

 boil slowly for about another half-hour, observing all 

 the while the level of the fluid, which should not fall 

 below the litre mark. It is necessary to reduce the tem- 

 perature of the mass to the point given, 68°-70° C; 

 otherwise the coagulation of the albumin will occur 

 suddenly in lumps and masses as soon as it is added, 

 and its clearing action will not be homogeneous. The 

 process of clarification with the egg is purely mechani- 

 cal — the finer particles, which would otherwise pass 

 though the pores of the filter, being taken up by the 

 albumin as it coagulates and retained in the coagula. 



At tlie end of one-half hour the boiling mass may be 

 easily and quickly filtered through a heavy, folded paper 

 filter at the room temperature, and, as a rule, the filtrate 

 is as clear and transparent as agar-agar usually appears. 



It might be well to emphasize the fact that for the 

 filtration of agar-agar a hot-water fininel, or any other 

 special device for maintaining the temperature of the 

 mass, is totally unnecessary. Agar-agar prepared after 

 the methods just given should filter through a properly 

 folded paper filter at the rate of a litre in from twelve 

 to fifteen minutes. 



Another plan that insures complete solution of the 



