114 BACTERIOLOGY 



use a much greater filtering surface is obtained, as it is in 

 contact with the funnel only at the points formed by the 

 ridges, leaving the greater part of the flat surface free for 

 filtration. 



The employment of the hot-water funnel, so often recom- 

 mended, has been dispensed with in this work to a very 

 large extent, for the reason that if solution of the gelatin 

 is complete, filtration is so rapid as not to necessitate the 

 use of an apparatus for maintaining a high temperature. 

 The temperature at which the hot-water funnel retains the 

 gelatin is so high that evaporation and concentration rapidly 

 occur, and in consequence filtration is, as a rule, retarded. 

 The filtration is frequently done in the steam sterilizer; 

 but this, too, is unnecessary if the gelatin is quite dissolved. 

 At the ordinary temperature of the room, and by the means 

 commonly employed for the filtration of other substances, 

 both gelatin and agar-agar may be rapidly filtered if they 

 are completely dissolved. 



It not infrequently occurs that, even under the most 

 careful treatment, the filtered gelatin is not quite trans- 

 parent, and clarification becomes necessary. For this 

 purpose the mass must be redissolved, and when at a tem- 

 perature between 60 and 70 C. an egg, which has been 

 beaten up with about 50 c.c. of water, is added. The whole 

 is then thoroughly mixed together and again brought to the 

 boiling-point, and kept there until coagulation of the 

 albumin occurs. The egg albumin coagulates as large floccu- 

 lent masses, and it is better not to break them up, 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 



