548 C. L. WILLIAMS AND H. P. LETTON 



the bottom. The result was more than a settling of the solid 

 particles, it was rather the ensnaring of these in a dehcate coagu- 

 lum, much like the coagulum of aluminum hydrate and like 

 that substance in requiring some time for its action. After the 

 formation of this flocculent precipitate a single filtration through 

 cotton produces a beautifully clear filtrate. 



The following points should be remembered. Any stirring be- 

 fore filtration will quickly break up the coagulum, which is very 

 dehcate, a cloudy filtrate resulting. For this reason, the reac- 

 tion should be adjusted before placing on the water bath, as we 

 have found that this changes very little during its stay there. 

 After sterihzation in the autoclave the medium remains clear if 

 soon cooled. If remelted for pouring plates it is clear at first, 

 but after standing some time in the water bath a second flocculent 

 precipitate forms, which however settles to the bottom so that 

 with careful handling the clear supernatant medium maybe 

 readily poured off. 



No attempt has been made by us to review the literature deal- 

 ing with this subject, so that we do not know if this procedure 

 has been described before. We have never seen it mentioned 

 however. Any one who has had to make any considerable 

 amount of agar will readily understand the value of so simple a 

 method of obtaining a clear product. We prefer this method 

 even to clearing with egg albumin, since the result is a clearer 

 medium although it takes more time to prepare. 



