DIPLOCOCCUS PNEUMONIA 353 



beyond reasonable doubt were dealing with the true pneumococcus, but 

 did not in any way associate the microorganisms they described with 

 lobar pneumonia. The solution of this problem was reserved for the 

 labors of A. Frankel 1 and Weichselbaum 2 who published their results, 

 independently of each other, in 1886, demonstrating beyond question 

 that the pneumococcus is the etiological factor in a large majority of 

 cases of lobar pneumonia. 



Morphology and Staining. The morphology of the pneumococcus is, 

 in general, one of the most valuable guides to its identity. 



When typical, the pneumococcus is a rather large, lancet-shaped coc- 

 cus, occurring in pairs, and surrounded by a definite and often wide 

 capsule, which usually includes the two approximated cocci without a 

 definite indentation opposite their lines of division. The pneumococci 

 may, however, occur singly or in short chains, and even fairly long 

 chains are not infrequently met with under artificial cultural conditions. 

 This may be chiefly due to the cultural conditions or may be a promi- 

 nent characteristic of certain strains. Apparently the capsules of or- 

 ganisms making up the chains are continuous; wavy indentations are 

 usually present, however, in the capsule of chains, and at times distinct 

 divisions are observed. 



The chief variations from the typical morphology consist either in 

 the assumption of a more distinctly spherical coccus type, or in an 

 elongation approximating the bacillary form. Under certain conditions 

 of artificial cultivation a distinct flattening of the organisms, particularly 

 of those making up chains, may be seen, and even the impression of a 

 longitudinal line of division, characteristic of many streptococcus 

 cultures, is not infrequently gained. 



The capsules under certain conditions, especially in artificial media, 

 may be absent or not demonstrable, and in certain strains capsules ap- 

 parently may not be present under any conditions. Practically any of 

 the 3escribed variations may dominate one and the same culture under 

 different or even apparently the same conditions of cultivation, and all 

 grades may occur in capsule development, from its typical formation 

 through all variations, to its total and apparently permanent absence. 



The presence or absence of capsules depends, to a large extent, upon 

 the previous environment of the pneumococci under observation. The 

 most favorable conditions for the development or preservation of the 

 pneumococcus capsule are found in the body fluids of man and animals 



1 A. Frankel, Zeit. f. klin. Med., x, 1886. 



2 Weichselbaum, Med. Jahrbiicher, Wien, 1886. 



