EXAMINATION OF BLOOD. l8l 



are inoculated directly from the syringe, tube, or pipette 

 containing the blood, the pointed end being pushed 

 through the cotton-wool plug (the surface of which 

 must be previously sterilised by having its projecting 

 portion burnt off in the flame) and the blood allowed 

 to flow drop by drop on to the surface of the 

 medium, the tube being turned so that each portion 

 of the medium is covered by a film of blood. If the 

 tube method is used and the blood has been allowed 

 to coagulate the tip of the glass tube carrying the 

 needle should be broken off with a sterile pair of 

 forceps or pliers. The culture tubes are then to be 

 inoculated for twenty-four hours at the body tempera- 

 ture and examined. If they are sterile they are to be 

 returned to the incubator and examined after a further 

 period. 



If colonies appear they are to be carefully examined 

 with a lens, and their characters noticed. The organ- 

 isms which will be most likely to develop are strep- 

 tococci, staphylococci, anthrax bacilli, pneumococci, 

 typhoid bacilli, the bacillus of plague, or the bacillus 

 coli ; the gonococcus may also develop, for it will 

 obtain the haemoglobin necessary for the development 

 from the blood itself. 



Streptococci form small white colonies which show no 

 tendency to run together to form a film. The centre of 

 each colony is more opaque than its periphery. 



Staphylococci form a more or less uniform film, the 

 colonies extending laterally and fusing together. The 

 growth is opaque, and is of a dead white, lemon, or 

 orange colour, according to the nature of the staphylo- 

 coccus present (albus, citreus, or aureus). 



Anthrax bacilli form small white colonies having the 

 " barrister's wig " appearance already described. 



