64 BACTERIOLOGY. 



large masses of coagulated albumin if it can be avoided, 

 as when broken up into fine flakes they clog the filter 

 and render filtration very difficult. 



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 

 disintegration of these masses into the finer particles, 

 which have the effect just mentioned. 



Under no circumstances is a filter to be used for these 

 purposes 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 contract- 

 ing are often entirely occluded by the finer albumin- 

 ous flakes which become fixed within them. In this 

 way the filter may become almost entirely occluded. 

 The preliminary moistening with water causes the 

 diminution of the size of the pores to such an extent 

 that the finer particles of the precipitate now rest on the 

 surface of the paper, instead of becoming fixed in Us 

 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 fiame for a minute or so ; in 

 this way one can detect if all the albumin has been 

 coagulated and when 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 is materially diminished. 



As soon as the gelatin is complete, whether it is 



