38 INTRODUCTION TO CYTOLOGY 



conditions. Only future research will permit an evaluation of the many 

 conflicting views on this subject. Of special interest will be the results 

 of studies to determine to what extent protoplasm may possess a micellar 

 structure comparable to that of many of its products (p. 179). The point 

 to be borne in mind at present is that the structure in any event is indis- 

 putably colloidal, and that our attempts to explain protoplasmic behavior 

 must be based on this fundamental fact. We shall proceed, then, with 

 the general conception of protoplasm as a complex system of many sub- 

 stances dispersed in the form of granules, globules, filaments, networks, 

 and plates, which thus expose an enormous area of reacting surface in 

 proportion to their volume. The system includes an extensive series of 

 thin films in the interfaces between the continuous and dispersed phases, 

 between the differentiated protoplasmic regions or organs, and around the 

 mass as a whole. 



Some of the activities of protoplasm which seem clearly to be condi- 

 tioned by its polyphase, film-partitioned organization may now be briefly 

 enumerated. ^^ 



A great many chemical substances coexist in protoplasm without inter- 

 acting until certain conditions prevail, whereupon interaction occurs 

 suddenly and extensively. This is thought often to involve films separat- 

 ing the different phases of the system. Under appropriate circumstances 

 the properties of these films are rapidly altered, allowing the substances 

 on either side to interact, and the volume and the velocity of the reaction 

 are due in large measure to the enormous area of reacting surface. The 

 films separating various regions within a protoplasmic mass permit the 

 localization of very diverse types of chemical activity within a small space 

 and the consequent differentiation of organs in which these activities are 

 then more efficiently carried on. A particularly important case of the 

 control of reactions through changes in colloidal films is seen in general 

 and local alterations in the permeability of the plasma membrane bound- 

 ing any unit mass of protoplasm, a matter to be discussed in the next 

 section. 



The effect of colloidal structure upon processes involving adsorption 

 is noteworthy. Substances are peculiarly subject to chemical change 

 when adsorbed at surfaces because of the special energy conditions present 

 there. Adsorption is frequently a necessary preliminary to chemical 

 reaction. In protoplasm there exists an ideal structural basis for such 

 "adsorption catalysis"; in fact, it seems that "the determination and con- 

 trol of chemical reactions by adsorption are universal in living proto- 

 plasm" (R. S. Lillie, 1923). It seems clear that a part of the catalytic 

 activity of enzymes is due to their colloidal state; indeed, it appears that 

 respiration itself is a surface reaction conditioned in this way (Warburg; 

 see, further, Beutner, 1933). These facts suggest why it is that certain 



" See Bayliss (1923) and R. S. Lillie (1923). 



