258 SPECIFIC MICRO-ORGANISMS 



nously into rabbits. Recently Lamar and Meltzer 1 have induced 

 typical lobar pneumonia in dogs by introducing cultures of the 

 pneumococcus into the bronchi. 



The pneumococcus is somewhat variable in form. In the 

 animal body it occurs in pairs of lance-shaped individuals with 

 the points directed away from each other, and the pair is surrounded 

 by a thick gelatinous capsule. 2 The organism is always Gram- 

 positive. In cultures the capsules are less well developed and 

 often cannot be demonstrated at all. The individuals are often 



FIG. 105. Pneumococcus, showing capsule, from pleuritic fluid of infected rabbit, 

 stained by second method of Hiss. 



less pointed and frequently resemble short bacilli in form. They 

 may remain attached together in chains of six to eight cells. 



Cultures may be obtained on ordinary media but they are 

 prone to die out quickly. Blood-agar, serum agar or ascitic-fluid 

 agar are the best solid media, but even with these weekly trans- 

 plantation is usually necessary. Broth to which serum or ascitic 



1 Journ. Exp. Med., 1912, Vol. XV, pp. 133-148. 



2 In demonstrating the capsules, the method of Hiss gives excellent results. 

 Spread some blood or tissue juice on a cover -glass and as soon as the film of moisture 

 has disappeared, fix the preparation by heat. Then stain with hot aqueous gentian 

 violet and wash off the dye with a 20 per cent solution of copper sulphate. Examine 

 in the copper solution. Blot the preparation, dry it in air and mount in balsam. 



