320 THE BEGINNINGS OF LIFE. 



living exhibit only very languid movements, which, as 

 movements, are quite indistinguishable from those that 

 the same Bacteria may display when they are really 

 dead 1 . Because the movements, therefore, are of this 

 doubtful character, some are apt, unfairly, to argue that 

 the Bacteria which present them are not more living 

 than are the minute particles of carbon obtained from 

 the flame of a lamp when they exhibit similar move- 

 ments. This, however, is a point of view which 

 becomes obviously misleading if too much stress is laid 

 upon it j and it is more especially so in this case, when 

 it can be shown that Bacteria which display the most 

 characteristic sign of vitality viz. c spontaneous' divi- 

 sion or reproduction at this time, almost always 

 exhibit such mere languid movements. It should 

 always be borne in mind, in fact, that mobility is not 

 an essential characteristic of living Bacteria^ whilst the 

 occurrence of the act of reproduction is the most indubitable 

 sign of their life-, so that any Bacteria which are almost 

 motionless, or which exhibit mere Brownian move- 

 ments, may be living, whilst those which spontaneously 

 divide and reproduce are certainly alive whatever be 

 the kind of movement which they present. 



1 Speaking of the organisms above mentioned, Prof. Wyman says : 

 ' Under certain circumstances, all signs of life may cease, but the infusoria 

 may still be alive. If, for example, they are developed in a sealed flask, 

 as soon as the organic matter convertible into infusoria is exhausted, 

 their activity ceases, and they remain dormant for many months ; we have 

 kept them in this way for a year ; but if fresh material is supplied to them 

 they at once resume their activity.' Loc. cit. 



