NUTRIENT GELATIN 115 



cloth, and then through paper, is not only superfluous, but 

 in most instances renders the process of filtration much more 

 difficult, because of the disintegration 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 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 entirely occluded by the 

 finer albuminous flakes which become fixed within them, 

 and filtration practically ceases. The preliminary moisten- 

 ing 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 centimeters 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 coagulated i. e., 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; otherwise 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 should be 

 sterilized, the mouth of the flask or the test-tubes containing 

 it having been previously closed with cotton plugs. It may 

 be sterilized by either the intermittent method with stream- 

 ing steam or by a single application of steam under pressure 



