THE^ JOURNAL OF PHARMACOLOGY. 253 



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 necessity of re-heating the mass I 

 distribute the solution in three or four filters, using coarse folded paper, 

 pass sufficient boiling water through each filter to wash away loose lint 

 and thoroughly heat the funnels just previous to commencing filtration of 

 the agar. With good paper and proper attention to detail, filtration is 

 usually accomplished 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 steril- 

 ized in mass and allowed to stand in the sterilizer with the light turned 

 low or out imtil the precipitate collects together at or near the bottom 

 of the flasks, when the agar may be re-heated and re-filtered ; this time 

 with the confident expectation that the filtrate will be and will subse- 

 quently remain transparent. Or, if preferred, the agar may be run ofi" 

 into cylindrical deposit glasses, sterilized therein, and allowed to stand 

 in the sterilizer, as before, until the sediment has settled to the bottom, 

 after which, the clear fluid may lie syphoned off, or allowed to cool 

 and cut off with a knife and the portion containing the sediment be 

 discarded, or filtered. 



Usually, on account of the liability to secondary precipitates, and be- 

 cause the agar is never so transparent when filtered immediately as it is 

 when the filtration is deferred until after the first sterilization, I do not 

 filter at once, but merely strain out the coarser flocculi by running the 

 medium through loosely packed cotton, sterilize in flasks, allow the flasks 

 medium through osely packed cotton, sterilize in flasks, allow the flasks 

 to stand in the sterilizer and slowly cool, and wait until the following 

 day before filtering through paper. Filtration is then still more rapid, 

 if care is taken to bring the temperature of the mass up to the boiling 

 point in the sterilizer before commencing the filtration, and the product 

 is always transparent. 



The coarser precipitates which occur on sterilization are usually due 

 to the coagulation of albumin which has escaped coagulation at the time 

 of the preparation of the medium ; hut the troublesome ones are of more 

 doubtful origin ; probably they consist, in the first place, of very fine 

 flocculi which pass through the filter on the first filtration, and, in the 

 second place, of salts whicli are held in solution during the first filtration, 

 but which as a result of changes in the reaction, oxidation, or because of 

 lessened solubility in the cold medium and their presence to supersatu- 



