214 



THE INFECTIOUS DISEASES. 



acute lobar pneumonia were first demonstrated by him. ' It is commonly 

 called simply the " pueumococcus. " 



Characters of the Micrococcus Lanceolatus. 



During their development these germs are distinctly spheroidal ; but in their ma- 

 ture condition they are apt to become slightly elongated or oval and are often a little 

 broader at one end than at the other, assuming a lanceolate form. They are very apt 

 to occur in pairs, and frequently are seen in short chains, rarely in long chains. Very 

 frequently, when growing in the living animals, the pneumococcus is surrounded by 

 a distinct, homogeneous capsule of varying thickness (see Fig. 100). This capsule does 

 not, as a rule, develop in artificial cultures. The coccus itself is readily stained by the 



FIG. 100. MICROCOCCUS LANCEOLATUS (Pneumococcus). Showing capsules. 



anilin dyes and retains the stain by Gram's method; tne capsule is not easily demon- 

 strated except by special staining methods. 



The pneumococcus has no spontaneous movement and grows but feebly at ordinary 

 room temperature. It grows much better at blood heat, forming on the surface of blood- 

 serum or on very slightly alkaline glycerin-agar plates faint grayish, dewdrop-like, 

 inconspicuous colonies, somewhat similar to those of Streptococcus pyogenes, but usu- 

 ally more delicate. In beef tea it forms at body temperature a faint whitish sediment 

 with slight turbidity of the fluid. As a rule, the cultures are prone to lose soon their 

 virulence and to die off early, but the virulence may be maintained by successive inocu- 

 lations in the rabbit. The organism may remain alive for a long time dried in the spu- 

 tum, in one set of experiments for more than seventy days. 



The serum of persons suffering from acute lobar pneumonia, as well as the serum of 

 lower animals artificially immunized to the Micrococcus lanceolatus, induces agglutina- 

 tion of the organism in broth cultures. Wadsworth has recently shown that by the 



1 It was discovered by Sternberg in saliva, and its pathogenic power demonstrated 

 some years before its full significance in connection with pneumonia was understood. 



