52 MORPHOLOGY OF THE BACTERIA. 



This is not, however, exactly the opinion of 

 Nageli, who seems to consider movement as the 

 surest distinctive characteristic. 



" There are," he says, " but three distinctive 

 signs which enable us to recognize with some 

 certainty that granules under observation are or- 

 ganisms, — spontaneous movement, multiplication, 

 and equality of dimensions, united with regularity 

 of form. 



"The most certain character is movement in 

 a straight or curved line, — a movement which 

 inorganic granules never present. One should 

 take care not to be deceived by movements 

 which are caused by currents in the liquid under 

 observation. Nor should one allow himself to be 

 deceived by the tremulous motion, called molecu- 

 lar movement, in which the granules do not really 

 change their position. These movements are seen 

 in most cells, and even in those of the Schizomy- 

 cetes, and inorganic bodies themselves present it. 



" Multiplication is a character less important 

 than movement. When among granules some 

 are found united in pairs, it may be supposed 

 with probability that division and multiplication 

 are taking place. When rods are bent at an angle, 

 one may predict their division in two parts. 



" Finally, as to size and form. Granules of dif- 

 ferent size and of a more or less irregular form 

 ought not to be considered as belonging to the 

 group of segmented fungi; if, on the contrary, 

 the granules offer dimensions perfectly equal, and 

 a spherical or oval form, the distinction is more 



