86 BACTERIOLOGY. 



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 commerce 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 carefully through- 

 out the agar-agar, and allow the mass to boil slowly 

 for about another half-hour, observing all the while the 

 level of the fluid. It is necessary to reduce the tempera- 

 ture of the mass to the point given, 68-70 C., other- 

 wise the coagulation of the albumin will occur suddenly 

 in lumps and masses as soon as it is added, and its clear- 

 ing action will not be homogeneous. The process is 

 purely mechanical the finer particles, which would 

 otherwise pass through the pores of the filter, being 

 taken up by the albumin as it coagulates and retained 

 in the coagula. 



At the 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 

 ally appears. 



It might be well to emphasize the fact that for the 

 filtration of agar-agar a hot water funnel, 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 agar- 

 agar without causing the precipitates that are commonly 

 seen when all the ingredients are added at first and 



