PNEUMOCOCCUS. 63 



pairs. The rest of the slide will be unstained, so that 

 you will not be able to make out the capsule. 



Now examine the carbol-fuchsin specimen. You will 

 see the cocci coloured a deep red, and you will also 

 notice that the general surface of the film is stained 

 pink, while there is a clear and colourless zone round 

 each pair of cocci. This is the capsule, which is 

 rendered distinct by " negative staining." If the 

 carbol-fuchsin has been allowed to act too long the 

 capsule may be stained a faint pink. 



INTERPRETATION OF RESULTS. 



In cases of lobar pneumonia you will probably find 

 pneumococci in great quantity, and no other bacteria in 

 a specimen of sputum made in the manner described. If 

 you find many pneumococci in a case of lobular 

 pneumonia the disease may have been caused by 

 another germ, and the cocci in question may have 

 been nothing more than a secondary infection. The 

 carbol-fuchsin specimen should be searched for bacilli 

 resembling those of influenza, &c., and another should 

 be stained for the tubercle bacillus if the clinical aspect 

 of the case suggests the possibility of a tubercular origin 

 for the disease. 



Pus is examined in the same way and presents similar 

 appearances. Most of the cocci are extra-cellular. 



The method of making a film from pus is described in 

 a subsequent chapter. It is very similar to that 

 described above, but the upper slide should be allowed 

 to fall on the lower one by its own weight ; the two 

 should not be pressed together. 



