112 BACTERIOLOGY. 



its 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 

 recommended, 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 evapora- 

 tion and concentration rapidly occur, and in consequence 

 filtration is, as a rule, retarded. The filtration is fre- 

 quently 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 sub- 

 stances, 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 perfectly 

 transparent (the condition to which it must be brought, 

 otherwise it is useless), and clarification becomes neces- 

 sary. For this purpose the mass must be redissolved, 

 and when at a temperature 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 

 albumin coagulates as large flocculent masses, and it is 

 better not to break them up if it can be avoided, as 

 when broken up into fine flakes they clog the filter and 

 materially retard filtration. 



