THE WORLD OF MICROSCOPIC LIFE 59 



only after a great deal of careful and critical work. 

 This is the specificity of these low forms of life. 

 Each kind of micro-organism breeds true to type, 

 maintaining, even amid considerable changes in the 

 course of its life cycle, certain structural features 

 characteristic of its species as well as its own pe- 

 culiar physiological activities. Several of the older 

 observers had very incorrect views concerning the 

 relationships and transformations of these primitive 

 forms of life. Thanks to the refinements and per- 

 fection of bacteriological technique the older errors 

 have been corrected. The most primitive organ- 

 isms fall into species just as the higher animals and 

 plants do. There is a certain amount of variation 

 or deviation from the type, to be sure, but this is 

 quite analogous to, and probably no more extensive 

 than the variability observed in higher organisms. 

 The more we know of primitive forms the more 

 closely are they found to resemble the highly de- 

 veloped types with which we are familiar. Life 

 is very much the same sort of thing wherever we 

 find it. 



