TEXT-BOOK OF BACTERIOLOGY. 279 



middle, but paler toward the margin and of a peculiar lustre. 

 Around the colony is a thick circular belt, appearing (on changing 

 the illumination) sometimes clear, sometimes dark, and formed by 

 the lateral walls of the hole-like depression in which the colony 

 rests. 



Deneke's vibrio is, therefore, macroscopically distinguished on 

 the plate from the cholera vibrio, by a more rapid liquefaction of 

 the gelatin, a quicker growth of the colonies, and their yellow col- 

 oring. Microscopically, by irregular form and the thick rampart 

 surrounding each. 



In the test-tube the same conditions obtain. The liquefaction 

 proceeds evenly along the entire inoculating puncture, but here too 

 the bacteria sink in coils to the bottom from the central parts of 

 the culture. They do this so completely that only a more exact 

 observation will exhibit development in this condition. There usu- 

 ally arises at the surface a yellowish, thin layer, above which fre- 

 quently hovers a funnel-shaped depression, a kind of " air- vesicle " 

 larger than that in cholera cultures. Then follows the path of 

 the inoculating puncture, which appears with a diffuse light as a 

 broad, shining canal ; finally, there are yellow heaps constituting 

 the principal mass of bacterial growth. The contents of the tube . 

 are wholly liquefied in about two weeks. 



Deneke's vibrio thrives on agar-agar as a thin yellowish coat 

 in the neighborhood of the inoculating line. 



It grows on potatoes at breeding temperature, as a delicate, 

 yellowish film in which may sometimes be noticed beautifully-formed 

 spirilla. 



It is remarkable that Deneke's vibrios possess pathogenic prop- 

 erties. With the method of infection used for cholera bacteria 

 Guinea-pigs may be killed, death ensuing in three animals out of 

 fifteen treated. 



X. VIBRIO METSCHNIKOFF (GAMALElA.) 



A micro-organism observed by Gamaleia and called " vibrio 

 Metschnikoff " is more nearly related to the comma bacillus than 

 the two kinds of bacteria just described. It was discovered in the 

 intestinal contents of poultry, especially of hens, and was repre- 

 sented as the original cause of a special affection of these animals, 

 possessing in its visible qualities much resemblance to chicken 

 cholera. It is said to occur more frequentty in Russia during the 

 summer months. 



The vibrio Metschnikoff is a curved bacterium whose single links 



