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 

 100 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, 



