66 BACTERIOLOGY. 



and then add the whites of two eggs which have been 

 beaten up in about 50 c.c. of water. Mix this carefully 

 throughout the agar, and allow the mass to boil slowly 

 for about one-half hour, observing all the while the level 

 of the fluid. It is necessary to reduce the temperature 

 of the mass to the extent given, 68-70 C., otherwise 

 the coagulation of the albumin will occur in lumps and 

 masses as soon as it is added, and its clearing action will 

 not be homogeneous. The process is a purely mechani- 

 cal one the finer particles, which would otherwise pass 

 through the pores of the filter, being taken up by the 

 albumin as it coagulates and retained in the coagula. 



At the end of one- half hour the boiling mass may be 

 easily and quickly filtered through a heavy, folded paper 

 filter at the room temperature, and, as a rule, the filtrate 

 is as clear and as transparent as agar-agar usually appears. 

 If the mixture is positively alkaline, it is not only cloudy, 

 but it filters with difficulty ; if it is acid, it is usually 

 quite clear ; but, as Schultz has pointed out, it loses at 

 the same time some of its gelatinizing properties. The 

 bouillon should always be neutralized before the agar- 

 agar is added to it, for the bouillon, which is normally 

 acid, from the acid of the meat, robs the agar, under 

 the influence of heat, of some of its gelatinizing powers ; 

 this cannot be regained by subsequent neutralization. 



Another method by which the agar-agar can easily 

 and quickly be melted, is by steam under pressure. If 

 the flask containing the mixture of bouillon and agar 

 be kept in the digestor or autoclav, with the steam under 

 a pressure of one atmosphere, as shown by the gauge, for 

 from twenty to thirty minutes, the agar-agar will be 

 found at the end of this time completely melted, and fil- 

 tration may then be accomplished with but little difficulty. 



