54 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



Examine your Gram specimen first. The pneumococci (which 

 will be almost black) should be clearly seen, and you should be 

 able to make out their shape and characteristic arrangement in 

 pairs. 



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," and 

 these appearances will be better seen in a somewhat thick and 

 deeply-stained film, though if the carbol fuchsin has been allowed 

 to act too long the capsule may be stained a faint pink. Occa- 

 sionally the capsule has a great affinity for carbol fuchsin, and 

 stains more deeply than the surrounding film, but this is unusual. 

 There are special methods of staining which may be used to 

 render the capsule more distinct, but these are usually unnecessary 

 for the diagnosis. 



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. A specimen should be stained 

 deeply by carbol fuchsin or methylene blue and searched for 

 bacilli resembling those of influenza, etc., and another should be 

 stained for the tubercle bacillus if the clinical aspect of the case 

 suggests the possibility of a tuberculous origin for the disease. 



Pus is examined in the same way, and presents similar appear- 

 ances. Most of the cocci are extracellular, but some are fre- 

 quently contained in the cells, and may then not retain Gram's 

 stain. 



It is not usually necessary to make cultures, as the pneumo- 

 coccus is readily recognized in pathological material from its 

 morphological appearance and staining reactions alone. Where 

 cultures are required, agar is about as good a medium as can be 

 used, and it must be incubated at the body temperature. The 

 colonies are visible after twenty-four hours as very small trans- 

 parent circular masses, which are but slightly raised and show 

 but little tendency to increase in size on further incubation. It 

 is a very delicate organism, and one which readily dies out on 

 ordinary media, so that if a culture is to be " kept going " it must 



