CUL 77 VA TION OF BA CTERIA . in 



the thorough solution of the agar-agar, it is filtered, just 

 as the gelatin was, through a carefully-folded pharmaceu- 

 tical filter wet with boiling water. It may expedite mat- 

 ters to pour in about one-half of the solution, keep the 

 remainder hot, and subsequently add it when necessary. 

 Experience shows that 1000 c.cm. of agar-agar rarely go 

 through one paper, and I always expect when beginning 

 the filtration to be compelled to boil the material which 

 remains on the paper again, and pour it through a new 

 filter. 



The formerly much-employed hot-water and gas-jet 

 filters seem unnecessary. If properly prepared, the whole 

 quantity will filter in from fifteen to thirty minutes. 



If made from beef-extract, the agar-agar almost always 

 precipitates a considerable amount of meat-salts as it 

 cools. This should be anticipated, but, so far as I can 

 determine, cannot always be prevented. The amount is 

 certainly lessened by making the bouillon first, filtering 

 it cold, then adding the agar-agar, and dissolving and 

 filtering it. 



The difficulty of filtering the agar-agar has led Fliigge 

 and others to adopt a method of sedimentation. An in- 

 genious apparatus for this purpose has lately been devised 

 by Bleisch. The methods can be simplified by using a 

 small pharmaceutical percolator, the bottom of which is 

 closed by a rubber cork containing a tube which extends 

 nearly to the top of the percolator and is attached to 

 a rubber tube with a pinchcock below. The melted agar- 

 agar is poured into this, and kept in the steam apparatus 

 until the sedimentation is sufficient to allow clear fluid to 

 be drawn from the top. As the clear agar-agar is drawn 

 off the tube is pulled down through the rubber cork, and 

 more drawn off until only the sediment is left. 



Agar-agar is dispensed in tubes like the gelatin and 

 bouillon, sterilized by steam by the intermittent process, 

 and after the last sterilization, before cooling, each tube 

 is inclined against a slight elevation, so as to offer an ex- 

 tensive flat surface for the culture. 



