8 



PHYSIOLOGY. 



in which were supposed to lie active properties of the cell. The 

 liquid, originally called plant-slime, was named protoplasm by von 

 Mohl, and was thought to be a waste-product. 



That the wall, or membrane, was not of vital importance was 

 clearly demonstrated by later researches. The study of the amoeba 

 and of the white blood-corpuscle, one-celled organisms, was the chief 

 means. These organisms are capable of extending their bodies into 

 processes fine threads and networks as they move about from 

 place to place, taking up and giving off matter as they go. They pos- 

 sess all the elementary vital functions, and yet at no time do they 

 possess a cell-membrane, showing that the protoplasm, not the mem- 



Cell-membrane 



Reticulnm of cell* 



Membrane of nucleus 



Nuclear achromatic 

 substance 



Nuclear chromatic 

 substance 



Fig. 2. Cell with Reticulum of Protoplasm Radially Disposed. From 

 Intestinal Epithelium of a Worm. (CAENOY.) 



brane, was the seat of the functions. An immense number of other 

 unicellular organisms were examined, together with the develop- 

 ment of other plants and animals, and many cells devoid of a mem- 

 brane were found. 



PROTOPLASM. 



The protoplasm of unicellular organisms appears as a viscid sub- 

 stance, which is almost always colorless and which will not mix 

 readily with water. The term protoplasm is constantly in the mouths 

 of the physiologists, and it is difficult to give it a rigid definition, 

 since it is used in so many different senses. Hence, we commonly 

 describe protoplasm as a living substance surrounding a nucleus, 

 which substance may or may not be limited by a cell-wall. 



