II. POWERFUL FORCE GENERATED BY PROTEIN POLYMERIZATION 49 



polymerization. When antigen molecule increases in size, molecules of 

 antibody combining with it seem generally to increase in number ; for 

 example, according to Heidelberger and Kendall (15), while a single 



^<^. 



Sr^ 



Free water 

 molecules 



— Surface of 

 a virus particle 



Fig. 8. Diagram of the long range force. 



molecule of serum albumin as antigen can combine only 6 molecules of 

 the antibody, thyroglobulin which is known to have molecular weight 

 about 10 times as great as that of serum albumin can combine 60 

 molecules. The increase in the molecular size of antigen can be looked 

 upon as the result of polymerization of unit molecules with the piling 

 up of the specific active groups. The accumulation of the monomole- 

 cular layers of antigen in the experiment of Rothen may be regarded 

 as the increase of the molecular size. 



The fact that virus activities are carried by particles having sizes 

 greater than a certain value may come from the requirement of 

 polymerization of protein molecules for the activities. If the polymeriza- 

 tion degree is low, though sufficient for acting as a virus, the virus 

 may be able to exhibit only a weak action and in addition unstable and 

 liable to be inactivated. 



According to our study, as described in Part I, Chapter III, small- 

 sized phage particles have the activity much less than that of large- 

 sized particles, and 50 or 100 small-sized particles seem to be compatible 

 in their activity to a single large-sized particle. This fact may be at- 

 tributed to the instability of the small-sized particles, but it seems a 



