122 BIOLOGY OF PNEUMOCOCCUS 



pneumococcus is obtained from the sputum by mouse test, it may 

 safely be considered the cause of the disease, but when a pneumo- 

 coccus which does not react specifically (type 4) is found in the 

 sputum, a second examination will in approximately 15 per cent of 

 the cases yield a specific reaction for one of the fixed types." 



Gundel 568 pointed out the various sources of error in the bac- 

 teriological diagnosis of pneumococcal infections. He recommended 

 the examination of successive specimens of sputum, mentioned the 

 difficulty presented by the presence of more than one type of Pneu- 

 mococcus in sputum, and explained the replacement of organisms 

 of the fixed types by those of the heterogeneous "X" (American 

 Group IV) by assuming that virulent Type I and II organisms 

 disappeared from the sputum as the pneumonic disease progressed, 

 thus allowing a predominance of pneumococci from the upper re- 

 spiratory tract. 



The reports cited above are introduced to emphasize the need 

 for thoroughness and care in the examination of infected material 

 submitted for pneumococcal diagnosis. In some specimens, a sin- 

 gle type of organism may be present and may so predominate that 

 its identification by any one of the methods is a simple matter. 

 When, however, pneumococci are few in number, or when variable 

 results occur, the sputum should be examined by other methods 

 and controlled by serological tests on cultures derived from single 

 colonies. 



In 1917, Blake 128 devised a method for obviating the difficulties 

 in the mouse test. He injected the mouse with sputum and, when 

 infection had sufficiently progressed, washed out the peritoneal 

 cavity with sterile saline solution, centrifuged the washings at high 

 speed, and to one part of the sterile supernatant fluid added an 

 equal part of diluted immune serum. When the organism was of the 

 same serological type as that of the serum a precipitate formed im- 

 mediately. Used with a large number of strains, Blake found this 

 test to be consistently positive and specific for Types I, II, and 

 III. The principle of the method lay in the liberation of soluble 



