l6 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



medium is not absolutely clear, but sufficiently so for most 

 purposes. 



The agar is again melted and placed in test-tubes ; these are 

 sterilized on three successive days and allowed to set in a sloping 

 position. For certain purposes glucose, glycerin, etc., 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, and is 

 best purchased ready for use from a good laboratory. It is used 

 chiefly in the diagnosis of diphtheria by the examination of 

 " swabs " from the throat. 



Potato tubes are in occasional use, and are easy to prepare. 

 The process is as follows : Take large and sound potatoes and 

 scrub them thoroughly with a nail-brush under the tap. Peel 

 them deeply enough to remove the eyes completely. Then cut 

 them into cylinders a little less than f inch in diameter (if you are 

 using |-inch test-tubes) and as long as possible ; this is best done 

 by means of a cork-borer, but they may be shaped by means of a 

 knife if this is not at hand. Then cut each cylinder in half by a 

 cut running obliquely from end to end ; the shape of each half 

 should be exactly like that of the medium in a sloped gelatin tube. 

 Place the halves in a large vessel of tap-water and allow them 

 to soak all night ; it is a good plan to use running water if 

 possible. 



After this has been done place each half (base downwards) in a 

 test-tube, having previously inserted a small mass of absorbent 

 cotton-wool and enough water to saturate it. Plug the mouth of 

 the tube with cotton-wool and sterilize on three successive days. 



INOCULATION OF CULTURE MEDIA 



The method in which this is done varies greatly according to 

 the end in view, and variations of the process now to be described 

 will be mentioned under their appropriate headings. We will 

 suppose that we have to examine a specimen of pus, and wish to 

 make a stroke culture on agar and a stab culture in gelatin. The 

 following must be at hand : 



1. The pus. 



2. A sloped agar tube and a stab gelatin tube. 



3. A Bunsen burner or a spirit-lamp with a tall flame. 



