60 PRACTICAL BACTERIOLOGY 



CIX. METHOD FOR HARD SUBSTANCES, FAVUS 

 CRUSTS, ETC. 



1. Sterilize a large watch-glass in the open flame and cover it up. 



2. Sterilize the bottom of an ordinary clean test-tube in the open 

 flame. 



3. Place a small quantity of sterilized bouillon on the watch-glass, 

 add the material to be investigated, triturate until thoroughly re- 

 duced and mixed with the bouillon, and proceed as in process No. 2, 

 previous method. 



CX. AGAR-AGAR PLATE METHOD. 



In making agar-agar plate cultures the fact must not be lost sight 

 of that this medium solidifies at 39 C. 



1. Melt three tubes of agar-agar at 90 C. (freshly prepared tubes 

 must not be used, as the water of condensation will cause all the develop- 

 ing colonies to run together). 



2. Place in a water-bath at 40 C., remove and inoculate quickly, 

 making the necessary series, O 1 2 . 



3. Pour the contents of the tubes preferably into Petri-dishes, or 

 if plates are used, without rims ; place a spot of melted sealing-wax at 

 each corner to prevent the agar-agar sliding off the plates. 



CXI. METHOD WITH ORDINARY AGAR-AGAR 

 IN TUBES. 



1. Take three freshly prepared tubes of oblique surface agar-agar 

 usually called c agar-slants ' with plenty of water of condensation in 

 the bottom. 



2. Inoculate only the water of condensation and transfer the 

 bacterial suspension to the water contained in the series of tubes, 

 making the usual number, O 1 2 . 



3. When the dilutions are completed, allow the water of con- 

 densation in each tube to flow gently over the oblique surface of the 

 agar medium, and place in the incubator at 37 C. 



CXII. BLOOD SERUM AGAR PLATE METHOD. 



1. Take three tubes of sterilized agar-agar, melt, retain fluid at 

 40 C. in a water-bath, inoculate, and make the usual dilutions, O 1 2 . 



