364 PROGRESS OF SCIENCE IN THE CENTURY. 



tury remained merely ajar till after the cell-theory 

 had been formulated. Since then the study of uni- 

 cellular plants and animals has been eagerly pur- 

 sued. From Dujardin and Ehrenberg to Haeckel 

 and Biitschli for Protozoa, from Pringsheim and 

 Cohn to De Bary for Protophytes, there was a con- 

 tinuous study of the simplest forms of life, and there 

 are many to-day who devote themselves to this study 

 and maintain that it is still only beginning. In 

 connection with bacteriology the names of Pasteur 

 and De Bary, Lister and Koch, Duclaux and Koux, 

 deserve particular mention. 



