BIOLOGY OF PNEUMOCOCCUS 35 



method described by Wadsworth* may be used to demonstrate 

 capsules in tissue sections. 



The capsules are indicative of the vigor and virulence of the 

 strain. They may best be seen "in the blood, serum and inflamma- 

 tory exudate of the infected rabbit and white mouse. They are 

 equally well marked in the fresh sputum of pneumonia patients, 

 especially in the early stages of the disease, and in the exudate ac- 

 companying such pneumococcus infections as meningitis, otitis 

 media and empyema."* 



The addition of blood, serum, milk, or other body fluids to nu- 

 trient media favors the development of the capsule under artificial 

 cultivation. 



Isolation of Pneumococcus 



ANIMAL INOCULATION 



One of the simplest ways of isolating pneumococci from infected 

 material is by mouse inoculation. If the source material is sputum, 

 a small portion can be washed in sterile broth or saline solution in 

 a Petri dish to remove the majority of accompanying mouth or- 

 ganisms. The washed sputum together with a small quantity of 

 broth is emulsified by grinding in a sterile mortar and the suspen- 

 sion in amounts of 0.5 to one cubic centimeter injected into the 

 peritoneal cavity of a white mouse. Just before or shortly after 

 death of the animal, the heart is exposed and, under sterile precau- 

 tions, punctured with a capillary pipette or hypodermic needle, 

 and the blood aspirated and planted in broth and on blood-agar 

 plates. In this way a pure culture can usually be obtained at the 

 first trial. Pieces of lung or other infected material may be treated 

 in the same manner as sputum. When it is suspected that few pneu- 

 mococci are present, the tissue may be macerated in broth and 

 given a preliminary incubation before the mouse injection. f 



* Zinsser and Bayne-Jones.is™ 



t For complete details of the method see Appendix. 



