20 . BACTERIOLOGICAL DIAGNOSIS. 
will take place, so that the fragments will not stick to 
the bottom and cause it to crack. When all is dis- 
solved the hot liquid must be carefully neutralised. It 
is then allowed to cool to about 50° C. and the white of 
an egg added for each 500 c.c. of fluid and mixed 
in thoroughly by being stirred with a glass rod. The 
whole is then placed in the steamer for an hour, at the 
end of which time the albumen should be completely 
coagulated. The beaker and its contents are then 
allowed to cool gradually, so that the coagulum (re- 
taining all solid particles) may settle to the bottom 
before coagulation is complete. Perhaps the best 
method of accomplishing this is to place it in the oven 
(taking care that the temperature does not exceed 
too° C.) after the fire has been raked out at night. 
In the morning the mass will be found to have solidified 
and there will be a coagulum at the. bottom. The 
beaker is then inverted and the mass ‘turned out” 
just as a cook turns out a jelly, and the sediment is cut 
off with a sharp knife. This avoids filtration, which is 
‘very troublesome. 
An alternative method is to filter the melted jelly 
through moistened filter paper or through two thick- 
nesses of butter-muslin. It is necessary to keep flask 
and funnel in a steamer (the water of which is kept 
boiling vigorously) during. the whole process, or the 
jelly will solidify in the outflow tube of the funnel. 
The agar is again melted and placed in test-tubes; 
these are sterilised on three successive days and allowed 
to set in a sloping position. For certain purposes 
glucose, glycerine, &c., are added to the agar. The’ 
addition should be made to the melted medium just 
before it is poured into the tubes. 
SOLIDIFIED BLOOD-SERUM is very difficult to prepare, 
