108 BACTERIOLOGY. 



were added has evaporated. Care must be taken 

 that the mixture does not boil over the sides of the 

 vessel. From time to time observe if the fluid has 

 fallen below its original level ; if it has, add hot water 

 until its volume of 1 litre is 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 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 dis- 

 solved 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 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 temperature of the mass 

 to the point given, 68-70 C., otherwise the coagula- 

 tion of the albumin will occur suddenly in lumps and 

 masses as soon as it is added, and its clarifying action 

 will not be uniform. The process of clarification 

 with the egg 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; as a rule, the 

 filtrate is as clear and transparent as agar-agar usually 

 appears. 



It may be well to emphasize the fact that for the 

 filtration of agar-agar no special device for maintaining 



