f' 



PATHOGENIC BACTERIA. 25! 



the line of puncture. On agar, round white colonies form, 

 not spreading. It produces a thick, slimy film on potato and 

 a broad, white, moist growth on blood-serum. This organ- 

 ism is only occasionally found in pus. It is pathogenic to 

 white mice and guinea-pigs, not to gray mice and rabbits. 

 It may produce a septicemia or only a localized suppuration 

 in guinea-pigs. In white mice a general septicemia results, 

 when the micrococcus tetragenus is found in the blood and 

 in the great viscera. White mice usually die in from two 

 to six days; guinea-pigs in from four to eight days. 



Micrococcus lanceolatus (Micrococcus pneumoniae crou- 

 posse, Micrococcus Pasteuri, Diplococcus pneumonise, Micro- 

 coccus of sputum septicemia, Streptococcus lanceolatus 

 Pasteuri, and Pneumococcus of Frankel). This organism 

 was discovered by Sternberg in his saliva in 1880, and after- 

 ward demonstrated to be the cause of lobar pneumonia by 

 Frankel and Weichselbaum. The micrococci usually occur in 

 pairs. The pair of micrococci, in its most typical form, ap- 

 pears like a couple of curved triangles with their bases close 

 to each other. The outline is usually described as being lan- 

 cet-shaped. The micrococci are frequently oval or round; 

 they often form chains. When it is most characteristic, each 

 pair of micrococci is surrounded with a capsule, which is 

 best shown in preparations made from the blood of infected 

 animals or from pneumonic sputum; the capsule is not 

 usually seen in preparations made from cultures. For 

 methods of demonstrating the capsule see page 57. The 

 pneumococcus is not motile. It stains by Gram's method, 

 which also is useful in demonstrating the capsule. It is 

 facultative anaerobic. It grows only at elevated tempera- 

 tures, preferably about 35 to 37 C. Gelatin is not lique- 

 fied. It grows well upon agar, upon blood-serum and upon 

 Guarnieri's medium (p. 81). It does not grow upon potato. 

 Milk usually becomes acid, and may or may not be coagu- 



