512 BACTERIOLOGY. 
and as obtained from the saliva it differs again 
from the organism when occurring in pneumonia. 
When grown on artificial culture media, variations in its 
morphology have been observed, at one time the indi- 
vidual cells being oval in shape and united in pairs, and 
then surrounded by a capsule; at other times spherical 
and arranged in longer or shorter chains, like strepto- 
cocci, and then being without a capsule. Variations 
in virulence have also been noted, both in the animal 
body in different stages of disease and when grown out- 
side the body on artificial culture media. These great 
variations in biological and pathogenic properties have 
induced some investigators to believe that there were 
several distinct species of this organism. 
These views, however, have not met with general 
acceptance. In an exhaustive investigation into the 
subject by Kruse and Pansini, who obtained the micro- 
cocci from the most varied sources—from the saliva in 
health and disease, from the nasal secretions, from pneu- 
monic sputum at different periods and phases of the 
illness, from the blood of different kinds of animals 
killed by inoculation, and, finally, from many primary - 
and secondary affections due to this organism—after 
carefully weighing their results from different points 
of view and comparing the morphological, biological, 
and pathological characteristics of the various micro- 
cocci found, these observers have come to the conclu- 
sion that ‘‘it is impossible to distinguish different 
varieties’? of pneumococci. They found numerous 
quantitative and qualitative variations in virulence, 
growth, power of resistance, etc., but at the same time 
such an inconstancy in these variations that they were 
unable to make any classification into separate varieties. 
