THE BIOLOGY OF THE CELL SURFACE 



theories based on a membrane of whatever hypothetical 

 physico-chemical composition. The presence of the fila- 

 ments means that the exposed cytoplasmic surface is 

 enormously larger than if there were only a smooth 

 membrane, and at the same time that it forms a sys- 

 tem of capillary spaces. But this surface is not merely 

 a static structure. The cytoplasmic processes which char- 

 acterize the ectoplasm are indeed fine pseudopodia and as 

 such display constant activity. By means of them the 

 cell has phagocytic power, ingests fine particles. Phago- 

 cytosis is- indeed an activity exhibited by all animal cells 

 and not only by Amoebae, white blood cells and fixed tissue 

 phagocytes as those in the vertebrate liver.^ The moment 

 that we appreciate the normal structure and behavior of 

 the ectoplasm, the problem of the entrance of water and 

 of solutions is placed in a new light. The theories of cell- 

 permeability with their discrepancies and conflicts can with 

 profit be abandoned. Since the ectoplasmic pseudopodia 

 respond actively to the environment they regulate the 

 exchange between cell and external medium. 



All these considerations and data indicate that the sur- 

 face-cytoplasm can not be thought of as inert or apart from 

 the living cell-substance. The ectoplasm is more than a 

 barrier to stem the rising tide within the active cell- 

 substance; it is more than a dam against the outside world. 

 It is a living mobile part of the cell. It reacts upon and 

 with the inner substance and in turn the inner substance 

 reacts upon and with it. It is not only a series of mouths, 

 gateways. The waves of protoplasmic activity rise to 

 heights and shape the surface anew. Without, the environ- 

 ment plays upon the ectoplasm and its delicate filaments 

 as a player upon the strings of a harp, giving them new 

 forms and calling forth new melodies. But these are too 

 nice for the undiscriminating ear of man. 



1 Cf. Geddes, iSSj. 



146 



