112 



CLINICAL BACTERIOLOGY AND H,MATOLOGY 



2. Preparation of Cultures. A good many culture media have been 

 used, and there is no decided agreement as to which is the bes.t. A 

 convenient and excellent medium is that devised by Messrs. Cole- 

 brook and Tanner, who take Douglas's trypsin broth agar (p. 9), melt 

 it, cool it to 45 to 50 C., and add 2 per cent, of sterile hydrocele 

 or ascitic fluid : blood-serum may also be used, and will be found more 

 convenient in many cases if only a small quantity is wanted, as suffi- 

 cient for two or three plates can easily be obtained from the finger. 

 This is mixed well in, and plates poured at once. The swab is rubbed 

 over the surface of a plate, or, better, over two, and it is an advantage 

 to dip it into the water of condensation on the lid of the plate between 

 each. Plates should be used as soon as they are set, and not allowed 

 to dry. 



3. Next day (after incubation) the plates are examined and all sus- 

 picious colonies noted, a film made from each (taking care not to 



FIG. 24. 



take the whole of the colony, but to leave enough for cultures if re- 

 quired) and stained by Gram, counterstained by neutral red. Char- 

 acteristic colonies to be picked out for examination are 2 to 4 milli- 

 metres in diameter, translucent, but with a granular centre and 

 sharply defined edges : they have a bluish opalescence when seen by 

 transmitted light. Colonies showing a yellow colour (various strains 

 of M. flavus) may be rejected, also any very small and transparent 

 colonies if the medium is a good one, and any opaque white ones. 

 In making your film you will find that the meningococcus and some 

 strains of the organism M. catarrhalis , with which it is most easily 

 mistaken easily make a uniform emulsion when rubbed up with a 

 drop of water on the slide. Where these two are in question cultures 

 should be made on the ordinary media, and incubated at 23 C. Most 

 strains of the M.' catarrhalis will grow, though badly; the meningo- 

 coccus, as a rule, not at all. 



Finally, if the identity of the organism is not clear, it must be 



