154 THE SCIENCE OF BIOLOGY 



Cells are the units of structural organization. All normal 

 functions are cell functions, and likewise all abnormal 

 activities. The value of such a generalization is apparent. 

 Its applications in medicine, in the problems of development, 

 in heredity, and throughout the field of biological science, 

 can be fully measured only by future accomplishment. The 

 cell-theory has unified facts of the most diverse nature and 

 has opened a way to the discovery of ultimate vital phenom- 

 ena. Outside the field of evolution, the recent progress of 

 biological science has been the progress of knowledge con- 

 cerning cells. Even heredity and variation are themselves 

 reducible to phenomena of the cell. 



