88 BACTERIOLOGY. 



fine flakes they clog the filter and materially retard 

 filtration. 



The practice sometimes recommended of removing 

 these albuminous masses by first filtering the gelatin 

 through a cloth, and then finally through paper, is not 

 only superfluous, but in most instances renders the pro- 

 cess of filtration much more difficult, because of the dis- 

 integration of these masses into finer particles, which 

 have the effect just mentioned, viz., of clogging the filter. 



Under no circumstances is a filter to be used without 

 first having been moistened with water. If this is not 

 done, the pores of the paper, which are relatively large 

 when in a dry state, when moistened by the gelatin not 

 only diminish in size, but in contracting are often en- 

 tirely occluded by the finer albuminous flakes which 

 become fixed within them, and filtration practically 

 ceases. The preliminary moistening with water causes 

 diminution of the size of the pores to such an extent 

 that the finer particles of the precipitate rest on the sur- 

 face of the paper, instead of becoming fixed in its meshes. 



During boiling it is well to filter, from time to time, 

 a few cubic centimetres of the gelatin into a test-tube 

 and boil it over a free flame for a minute or so; in this 

 way one can detect if all the albumin has been coagu- 

 lated — i. e., if the solution is ready for filtration. 



Gelatin should not, as a rule, be boiled over ten or 

 fifteen minutes at one time, or left in the steam sterilizer 

 for more than thirty to forty-five minutes, otherwise its 

 property of solidifying may be impaired. 



As soon as the gelatin is complete, whether it is re- 

 tained in the flask into which it has been filtered or 

 decanted off into sterilized test-tubes, it should be ster- 

 ilized in the steam sterilizer on three successive days, 



