574 PATHOGENIC BACTERIA. 



kept at 2)7° C., some of the colonies have a diameter of 

 2 to 3 mm. They are round in shape, with an even con- 

 tour, slightly raised above the surface of the agar-agar, 

 and smooth and shining in appearance. On holding up 

 the tube and examining such colonies by transmitted 

 light the centre of each is seen to be yellowish in color, 

 while the periphery appears bluish-white. On looking 

 at the same colonies by reflected light, no appearance of 

 yellow can be seen ; they then appear to be milky-white 

 in color. The separate colonies on the surface of the 

 agar-agar do not extend indefinitely, and after a couple 

 of months are found to be no larger than hemp-seeds. 



When kept at 25 C. the colonies do not become visi- 

 ble to the naked eye before the seventh day ; at 37° C, 

 about the third or fourth day. 



There is scarcely any growth in gelatin and no lique- 

 faction of the medium takes place. 



No growth takes place on boiled potato. 



Plate-cultures are not adapted to the study of the 

 organism because of the extreme slowness of its growth. 



The micro-organism seems to be constantly absent 

 from the circulating blood. Hughes has, however, cul- 

 tivated it from the heart's blood of a dead monkey. 



Bruce not only succeeded in securing the micro- 

 organism from the cadavers of Malta fever, but has also 

 obtained it during life by splenic puncture. 



The micro-organism is not pathogenic for mice, guinea- 

 pigs, or rabbits, but is fatal to monkeys when agar-agar 

 cultures suspended in water are injected beneath the 

 skin. 



The natural occurrence of the micrococcus and the 

 sources of contagion are unknown, and, as Bruce points 

 out, would be very difficult to determine because of the 

 high temperature at which development takes place, the 

 extreme slowness of its growth, and the absence of well- 

 marked morphological, cultural, or pathogenic charac- 

 teristics by which it could. be recognized. 



1 See Lancet, 1897, i., p. 656. 



