16 THE AMERICAN MONTHLY [Jan 



tion — which now should have cooled sufficiently not to 

 coagulate the albumin in the fresh-water, but still be hot 

 enough to remain fluid — and carefully neutralize with a 

 4 per cent solution of caustic soda. 



After neutralization boil the mixture until all the coag- 

 ulable albumin in the fresh-water has been coagulated 

 and comes to the surface, leaving a clear fluid beneath. 

 Again test the reaction, and, if need be, correct it ; add 

 sufficient boiling water to supply any loss that may have 

 occurred through evaporation, and filter through paper. 

 To insure rapid and complete filtration without the neces- 

 sity of reheating the mass I distribute the solution in 

 three or four filters, using coarse, folded paper, pass suf- 

 ficient boiling water through each filter to wash away loose 

 lint and thoroughly heat the funnels just previous to com- 

 mencing the filtration of the agar. With good paper and 

 proper attention to detail filtration is usually accomplish- 

 ed in from ten to fifteen minutes. 



While filtration is in progress sterilize or boil a tube of 

 the filtrate. If it remains clear after heating, and when 

 cold is free from sediment and only slightly opalescent, 

 the entire filtrate may be immediately run off into tubes 

 and sterilized. But if a precipitate should make its ap- 

 pearance either on heating or while cooling, the filtrate 

 should be sterilized in mass and allowed to stand in the 

 sterilizer with the light turned low or out until the pre- 

 cipitate collects together at or near the bottom of the 

 flasks when the agar may be reheated and refiltered ; this 

 time, with the confident expectation that the filtrate will 

 be and will subsequently remain transparent. Or, if pre- 

 ferred, the agar may be run off into cylindrical deposit 

 glasses, sterilized therein, and allowed to stand in the 

 sterilizer, as before, uutil the sediment has settled to the 

 bottom after which the clear fluid may be syphoned off, 

 or allowed to cool and cut off with a knife and the portion 

 containing the sediment be discarded, or filtered. 



