THE CELL AND PROTOPLASM. 



89 



discovered human being as forming the essential 



part of his nature. It was soon evident that this 



position could not be maintained. It was found 



that many bits of living matter were entirely 



destitute of cell wall. 



This is especially true 



of animal cells. While 



among plants the cell wall 



is almost always well 



developed, it is very 



common for animal cells 



to be entirely lacking in 



this external covering 



as, for example, the 



white blood-cells. Fig, 



22 shows an amoeba, a 



cell with very active 



powers of motion and 



assimilation, but with no 



cell wall. Moreover, 



young cells are always 



more active than older 



ones, and they com- 



i r, T FIG. 22. An amoeba. A single 



monly possess either no C eii without ceii waii. is 



cell wall or a very Blight 

 one, this being deposited 

 as the cell becomes older and remaining long after 

 it is dead. Such facts soon disproved the no'.ion 

 that the cell wall is a vital part of the cell, and 

 a new conception took its place which was to 

 have a more profound influence upon the study 

 of living things than any discovery hitherto made. 

 This was the formulation of the doctrine of the 

 nature of protoplasm. 



