AGAR MEDIA. 39 



pletely dissolved. The reaction of the material is now adjusted 

 according to the directions given under i (a). Previous to nitra- 

 tion the medium has to be clarified, and to accomplish this the 

 pan is removed from the fire and its contents cooled down to 

 60 C., and to them are added the yolks and whites of two 

 eggs beaten up gently in 100 c.c. of water. The pan is replaced 

 upon the fire, and with a low burning flame the heat of the pan 

 is to be gently and carefully raised to the boiling-point, so that 

 the coagulation of the eggs may be produced gradually. After 

 coagulation is completed, it is important to boil the agar gently 

 for about ten or fifteen minutes to allow the surface coagulum 

 to toughen sufficiently so that it will not readily disintegrate 

 when the agar is poured into the funnel containing the filter 

 paper. Before filtering, the pan and contents must be weighed, 

 so that, deducting 50 grammes for each egg 

 and the weight of the pan itself, the net result 

 will be 1000 grammes. Filtration is now 

 readily accomplished by using Swedish filter 

 paper of moderate thickness folded and 

 placed in a wire funnel, such as shown in 

 Fig. 8, to prevent contact with the walls 

 of the glass funnel into which it is placed, FIG. s.- wire funnel for 



supporting paper filter. 



and moistened thoroughly. To the lower 

 end of the glass funnel is affixed about 10 cm. of rubber 

 tubing of proper calibre carrying a pinchcock and a glass 

 delivery tube drawn out to a moderately fine bore. The appa- 

 ratus is now set up on a stand and the hot agar poured carefully 

 into the paper filter, the coagulum being held back by a small 

 oval strainer mounted on a handle, or by a large spoon. The 

 agar rapidly at first makes it way through the paper into the 

 glass funnel, when it is at once delivered into sterile tubes in 

 quantities of 12 c.c., or thereabouts; later on because of cooling 

 and plugging of the pores of the paper by small particles of 

 coagula, the agar comes through slower and slower, so that it- 

 is then necessary to empty it into the pan to be heated up and 

 again poured into a fresh filter ; this procedure being repeated 

 as often as necessary. Filtration may also be accomplished by 

 passing the hot agar through absorbent cotton packed not too 

 tightly into the neck of a glass funnel and wetted, or we may 

 have recourse to the use of a hot-water funnel (Fig. 9). 



