130 ELEMENTARY CHEMICAL PROCESSES 



Figure 1 is a schematic representation of a biological particle in its 

 aqueous sheath. The region ABC within the solid line is the particle 

 itself. The region D includes all that aqueous layer in which primary 

 creation of ions has a resultant chemical effect on the particle. The 

 region AB (not necessarily continuous) is the sensitive part of the 

 particle. It includes (or may be) the group injury to which is made 

 apparent by a change in the detectable behavior of the particle. The 

 region C is effectively inert; that is, injury, or a hit, within it is not made 



Fig. 1. Schematic representation of a biological entity. A, Hits in this region are 



always effective; B, hits in this region are sometimes effective; C, hits in this region 



are never effective; D, ambient layer of fluid in which hits may be effective. 



apparent by a change in detectable behavior; as a matter of experi- 

 mental fact it may be non-existent. The region A includes several 

 portions : 



(a) That volume which may be directly affected by radicals produced 

 in the layer D or by changes in the pH of that layer. 



(6) That volume which may transfer ionic charge to the layer D and 

 thus make it chemically active. 



(c) That volume in which untransferred ionic charge leads every time 

 to damage in the region A or B. 



In reference to this last point we must make some note of the elemen- 

 tary processes of the Franck-Rabinowitch cage effect. Neutralization of 

 an ion deep in the cage will not necessarily result in decomposition; that 

 is, the ion-pair yield may be less than unity both because of energy dis- 

 sipation (from the excited molecule A*) without primary decomposition 

 and because of primary recombination of radical (as distinguished from 

 molecule) products while still within their mutual range of influence. 

 In the region B the ion-pair yield is less than unity. On the other hand, 

 as intimated in (c) above, part of the decomposition in B may be the 

 result of a primary physical effect in A ; cf . the effect of absorption of 

 energy in an aromatic ring on decomposition in a side chain. 



A feature to be emphasized in consideration of Fig. 1 is the precise 



