NOT DESCRIBED IN PREVIOUS SECTIONS. 485 



at 37 C. and does not develop at temperatures below 15 C. In agar plates, 

 at 37 C., small, punctiform colonies are developed at the end of twenty-four 

 hours; these do not increase in size later; under the microscope the deep 

 colonies are seen to be spherical, granular, and dark yellow in color ; the 

 superficial colonies are more or less round, with irregular outlines, trans- 

 parent, slightly granular, and often have a shining nucleus at the centre. 

 Upon gelatin plates the colonies have a similar appearance, but are not vis- 

 ible in less than four or five days. In streak cultures upon the surface of 

 agar small, punctiform colonies are seen along the track of the needle at the 

 end of twenty-four hours, resembling fine dewdrops; the following day 

 these colonies are a little larger and less transparent; they remain distinct, 

 especially along the margins of the line of growth. Upon potato a very 

 thin, transparent layer is developed, which does not change the appearance 

 of the surface of the potato, but slightly increases its resistance to the plati- 

 num needle. In bouillon small flocculi. suspended in the clear liquid, are 

 developed within twenty -four hours; these subsequently sink to the bottom. 



Milk is not coagulated by this bacillus, and no gas is produced in media 

 containing sugar. 



Pathogenesis. Pathogenic for rabbits, guinea-pigs, young rats, and mice, 

 in which animals it produces general infection, and death- in rabbits at 

 the end of twenty-four hours. The bacillus is found in the blood in great 

 numbers. 



97. PROTEUS VULGARIS. 



Obtained by Hauser (1885) from putrefying animal substances, 

 and since shown to be one of the most common and widely distrib- 

 uted putrefactive bacteria. This and the other species of Proteus 



FIG. 156. Proteus vulgaris; '* swarming islands " from a gelatin culture. X 285. (Hauser.) 



described by the same bacteriologist (Proteus mirabilis, Proteus Zen- 

 keri) have no doubt frequently been encountered by previous observ- 

 ers, and are among the species formerly included under the name 

 66 Bacterium termo," which was applied to any minute motile bacilli 

 found in putrefying infusions. 



Morphology. Bacilli with rounded ends, about 0.6 // broad, and 



