30 MORPHOLOGY 



of the bacterium and the temperature of the surrounding 

 medium. The faculty of moving about from place to place 

 is possessed by only a few varieties of cocci, e.g. Micrococcus 

 agilis, etc., but is quite common among the bacilli and 

 spirilla. Motile bacteria progress by means of the vibration 

 of long, whiplike appendages called flagella or cilia. 



Ehrenberg was the first to describe flagella on bacterial 

 cells. In 1838, he described appendages on B. triloculare. 

 In 1870, Cohn described flagella on Spirillum volutans. In 

 J 875, Warming described flagella on Spirillum undula, Spiril- 

 lum rugula, etc. In 1877, various stains were used to dem- 

 onstrate their presence. By means of stains it was found 

 that a large number of bacteria possessed these organs of 

 locomotion. By the year 1880, all bacteriologists had agreed 

 that there were appendages of this character on certain 

 bacterial cells. The method of locomotion by flagella is 

 used by practically all motile lower bacteria. Among some of 

 the higher bacteria the existence of an undulating membrane 

 is claimed in certain species, e.g. Beggiaotoa. It is supposed 

 that these species move by the alternate contraction and re- 

 laxation of their undulating membrane. 



The flagella on a bacterium vary in riumber and arrange- 

 ment according to the species. They are usually quite con- 

 stant in number for the species. The flagella may vary in 

 position on the different bacteria, and Messea, in 1890, 

 proposed dividing the flagellate bacteria into the following 

 classes : 



