106 BACTERIOLOGY. 



as when broken up into fine flakes they clog the filter 

 and materially retard filtration. 



The practice sometimes recommended of removing 

 these albuminous coagula by first filtering the gelatin 

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

 superfluous, but in most instances renders the process 

 of filtration much more difficult, because of the disin- 

 tegration of the masses into finer particles, which have 

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



Under no circumstances should a filter be used with- 

 out 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 

 surface 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.j if the solution is ready for filtration. 



Gelatin should not, as a rule, be boiled more than 

 ten or fifteen minutes at one time, or be left in the 

 steam sterilizer for more than thirty minutes ; other- 

 wise its property of solidifying may be impaired. 



As soon as the preparation of the gelatin is complete, 

 whether it is retained in the flask into which it has 

 been filtered or decanted into sterilized test-tubes, it 



