CLASSIFICATION OF PNEUMOCOCCI 131 



estimating the degree of absorption, distribution, and neutraliza- 

 tion of injected pneumococcal antibodies. 



Another variation of the precipitin method was that described 

 by Sia and Chung (1932). 1271 They seeded cultures into poured 

 plates of dextrose-beef-infusion agar containing, in separate Petri 

 dishes, type-specific serums. After incubation, when the type of or- 

 ganism and serum corresponded, a well-defined annular opacity 

 surrounded each colony, an appearance which proved to be type- 

 specific. The method is obviously somewhat limited in value. It re- 

 quires discrimination in the quantity of inoculum as well as in the 

 amount of serum to be added and since, with these disadvantages, 

 it also requires twenty-four hours' incubation and large supplies of 

 immune serum, there is no reason for selecting it instead of the less 

 complicated and more rapid methods. In the same year, Petri 1084 

 described a procedure which he used in the study of pneumococcal 

 dissociation, but which, because of the recent development of sim- 

 pler techniques, has not been adopted. 



QUELLUNG PHENOMENON 



The latest method to be generally used is based on the Quellung 

 effect first described by Neufeld 974 in 1902. It promises to super- 

 sede all the previous rapid precipitation and agglutination meth- 

 ods. The technique as reported by Neufeld and Etinger-Tulczyn- 

 ska 988 consists in placing on a slide, separately, three loopfuls of 

 the sputum to be examined, with two loopfuls of undiluted type- 

 agglutinating rabbit serum on each drop of sputum, and then the 

 same amount of Loeffler's methylene blue. Each drop of the mix- 

 ture is covered with a cover-glass, and examined at intervals for 

 five to thirty minutes through an oil immersion lens. When the 

 type of the serum and of the pneumococcus are the same, the cocci, 

 stained blue, are seen surrounded by swollen capsules. The cap- 

 sules are a pale greenish-gray with a characteristic ground-glass 

 appearance, and are distinctly outlined by a thin, dark line around 



