THE CELL 15 



The walls were considered the important feature, and the 

 term cell meant the space enclosed by the wall. All this 

 was very natural, for botanists had quite generally, up 

 to this time, devoted their best energies to studpng the 

 form and structure of plants, paying relatively little at- 

 tention to their life functions, or physiology. Gradually, 

 however, it came to be recognized that the really impor- 

 tant part was the substance that filled the little compart- 

 ments in all living tissues.^ It finally came to be under- 

 stood that this is the only living substance in plants 

 (and in animals as well) , and that the cell-walls, and in 

 fact the entire organism, are built up by the activity of 

 this remarkable substance. It was first called by several 

 different names, but Hugo Von Mohl, a noted German 

 botanist, called it protoplasm,^ considering it as the first 

 organic substance formed from the inorganic materials 

 taken in by the plant. This name was generally adopted 

 by both botanists and zoologists. 



22. The Cell-theory.— The idea that all living things 

 are composed of cells, that the cell is the unit of plant and 

 animal structure, and that the essential thing about the 

 cell is the protoplasm, was elaborated by Schleiden (1838) 

 (for plants) and by Schwann (1839) (for animals), and 

 was accepted as generally correct by all students of plants 

 and animals. This doctrine became known as the cell- 

 theory of Schleiden and Schwann. The term cell is now 

 used in biology chiefly to designate the protoplasm comprised 

 within the cell-wall. A cell, then, is not a compartment 

 containing something, but is a structural unit of living 



^ An intimately connected layer, group, or body of similar cells, all 

 having like functions, is a tissue. 



* Greek protos (first) -|- plasma (thing formed). 



