Molecular Structure in Protoplasm 71 



seems probable that many vital activities take place in such or- 

 ganized structures. 



With this conception of aggregates in which protein molecules 

 with attached smaller organic molecules are in turn held together 

 by cohesion forces of the same sort, hydrogen bridges, ionic bondings, 

 and van der Waals' forces, the enormous number of submicroscopic 

 granules in the fluid cytoplasm begin to take on the suggestion of 

 individual characteristics. Some may be too small or too simple 

 to perform any particular activity; others, although complex enough, 

 may be nonfunctional because they do not contain the proper con- 

 stituents or because of unsuitable arrangement of the constituents; 

 while some are definitely functional in character. A functional ag- 

 gregate is comparable to a large "floating laboratory" in which a 

 variety of separate, although coordinated projects are being carried 

 out. 



Throughout this discussion, in which we have been concerned 

 with the molecular components of protoplasm and with the manner 

 in which their constituent atomic and molecular groups would allow 

 them to fit together, we have made use of the "particle" as a means 

 of keeping the molecular characteristics constantly in sight; and al- 

 though this has been a convenient means, it is based on in vitro 

 experimentation almost exclusively. The obvious question of the 

 biologist is: To what extent is it applicable to the living state? The 

 principal difference seems to lie in the random nature of the in vitro 

 world and the organization of the materials in the in vivo world; 

 further, in the living cell the functional aggregates are formed in 

 the presence of organized structures, of pre-existing mechanisms or 

 patterns. 



We have come to a point where we wonder whether the elemen- 

 tary molecules interact simply by chance as recognized by statistical 

 methods or, instead of this freedom, have some orderliness brought 

 into their relationships by restrictions imposed upon them by their 

 living environment. The nature of this orderliness in construction 

 must be consistent with the behavior of the living cell, and our way 

 of thinking must now be altered to include the biological, as well as 

 the chemical-physical, statistical point of view. At this stage it now 

 becomes a matter of not what possible things can happen to protein 

 particles and to the other component molecules to transform them 

 into protoplasm, but instead, what has happened to bring about the 

 construction of active protoplasm from which these organic mole- 

 cules were obtained. 



