I CYTOPLASM 159 



protein macromolecules, submicroscopic and even microscopic pro- 

 tein particles which bridge submicroscopic distances. Such reactions 

 occur when rod-shaped virus particles (Fig. 84c, p. 126) take a parallel 

 orientation in a concentrated sol (Wyckoff, i947a-c), when protein 

 macromolecules aggregate according to the rule of Svedberg (Fig. 

 84b) or when globular submicroscopic particles crystallize (Fig. 84 d). 

 Similar attractions over considerable distances appear when antibodies 

 (precipitins, agglutinins) cause the precipitation of specific proteins 

 or even the agglutination of bacteria and blood corpuscles. 



The nature of long-range forces is difficult to understand. As their 

 radius of action is greater than 50 A, they play an important role in 

 the structural arrangement of colloidal particles. Oster (195 i) shows 

 that long-range orientation is partly due to the repulsive effect of 

 electrical double layers in highly concentrated sols, and partly to 

 ordinary Van der Waals attractive forces which are additive, so that 

 an integrating effect of all the atoms of two adjacent macromolecules 

 is involved. 



ROTHEN (1947) has published experiments indicating that the action 

 of long-range forces is detectable at distances of over 200 A. He 

 coated the antigen of bovine albumin on a slide with a layer 200 A 

 thick of barium stearate and was able to observ^e the immunological 

 reaction of the antibody applied to this film. Even enzymes such as 

 trypsin and pepsin were found to act upon substrate layers through 

 an inert screen. The last experiment is in contradiction to the current 

 conception of enzyme action, which is considered to be a contact 

 reaction with the molecules of the substratum. The impermeability of 

 the intervening stearate films has therefore been doubted (Trurnit, 

 1950). Whatever the result of this criticism may be, long-range forces 

 incontestibly cause the aggregation of submicroscopic particles in sols 

 and the formation of structures in gels. 



There must be a discrete number of spots on the surface of a 

 globular macromolecule where junctions are possible. If this number 

 is two, the protein globules have a tendency to form beaded chains 

 (Fig. 104), which may yield a loose reticulum. If the number of active 

 spots is three, they will be the origin of a two-dimensional layer repre- 

 senting a porous film (Fig. 104). Four junctions would cause a three- 

 dimensional framework, since they are arranged rather in a tetrahedral 

 manner than in a plane. A sphere may touch as many as 6 neighbours 



