124 CLINICAL BACTERIOLOGY AND HiEMATOLOGY 



volume, to remove it from the rest of the fluid, allowing all that will 

 to drain away, and then to digest the fibrinous mass in an artificial 

 digestion mixture (pepsin and 0-2 per cent. HCl) until completely 

 dissolved. The resulting fluid is now centrifugalized or allowed 

 to stand for a day or so (in which case some thymol should be 

 added to prevent excessive growth of bacteria), and films prepared 

 from the deposit, which will contain the tubercle bacilli. The 

 advantage of this method is that all the bacilli in four or five 

 ounces of pleuritic fluid may be entangled in the clot, and con- 

 centrated into a comparatively small bulk. The tubercle bacilli 

 resist peptic digestion for a long time, but other organisms do 

 not, and the method is not available for them. 



Purulent pleurisies (empyemata) may be caused by many 

 organisms, the most common being the pneumococcus, strepto- 

 cocci, staphylococci, and the tubercle bacillus. 



The pneumococcus is readily demonstrated by a microscopical 

 examination, the method to be employed being the same as that 

 previously described. 



The pus in these cases is thick and creamy, and of a greenish 

 colour ; after it has stood for some time a thin layer of a greenish 

 fluid appears upon the surface. 



When an empyema is due to the pneumococcus alone, no other 

 organisms being present, the prognosis is distinctly better than in 

 cases in which other organisms are present, and the patient often 

 recovers after simple aspiration. This is especially the case in 

 children, in whom empyema is due to this organism in a very 

 large number of cases, certainly over go per cent. 



If cultures are made in pneumococcic cases, it may be noted 

 that occasionally very few of the organisms appear to grow into 

 colonies, as far as can be judged by a comparison between the 

 numbers of cocci present in the films and of colonies on the tubes. 

 This indicates that the majority of cocci are dead, and this makes 

 the prognosis better. The prognosis is also good in cases in which 

 very few cocci are present, and in those in which the cocci that 

 are present are largely contained in the leucocytes ; in this case 

 they may lose their power of retaining Gram's stain. 



The streptococcus is also readily demonstrated by a simple micro- 

 scopical examination; it grows readily on agar, forming small 

 round colonies, which do not tend to coalesce and are more opaque 

 in the centre than at the periphery. 



The pus is not generally very thick, and has a yellow colour 



