NUTRIENT GELATIN. 87 



as tightly folded as possible, without tearing it. The 

 advantage of the folded filter is that by 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 majority of the flat surface free for filtra- 

 tion. 



The employment of the hot-water funnel, so often 

 recommended, has been dispensed with in this work to 

 a very large extent, as we know that, if the solution of 

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

 necessitate the use of an apparatus for maintaining the 

 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 

 the 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 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 in which it must exist, other- 

 wise it is useless), and clarification becomes necessary. 

 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. It 

 is better not to break up the large masses of coagulated 

 albumin if it can be avoided, as when broken up into 



