104 John B. Calhoun 



Let: 



Ba = 1.0 be the value of this factor in all members of [Na]. 

 Bp = he the value of this factor in all members of l^Np]. 

 aaa represent the refractory period resulting in each of two members of 



[_Na] who meet. 

 a,rp represent the refractory period resulting in each member of [^Na'] 



which encounters a member of [A^p]. 

 aj,a represent the refractory period resulting in each member of [iVp] 



which encounters a member of [_Na]. 

 app represent the refractory period resulting in each of two members of 



[_Np^ which meet. 



It follows that: 



iaia = oiaaBa = idp = dapBa, aud all are real values (36) 



and that: 



^p^a ^pa-*^p ^p^p ^pp^ p V7 \*J i ) 



In all following discussion Ba and Bp will be omitted in discussing a, 

 but every mention of aaa and Uap will assume the action of Ba, and likewise 

 any mention of apa and app will assume the action of Bp. 



It may be objected that no distinction is being made between the two 

 kinds of contacts, responsive-responsive, and responsive-refractory. It is 

 perfectly feasible to introduce two refractory periods, aaa and aap, of differ- 

 ent duration to answer this objection. At the present juncture the experi- 

 mental data are so scanty that it does not appear to be fruitful to introduce 

 additional complexity, and we have chosen to consider ana = cinp for the 

 workmg model insofar as duration is concerned. 



An alternative model would have been to choose aap = 0, that is, the 

 only contact inducing a refractory period being a contact between two 

 individuals both of whom are responsive. Under such an assumption the 

 number of contacts between responsive individuals in a unit interval of 

 time w^ould increase asymptotically to the value 1/a, whereas, as we shall 

 show, the model adopted provides that the number of contacts between 

 responsive individuals passes through a maximum as A^ increases. 



Given sufficient proximity of an individual in the responsive state to 

 some other indi\'iduals requisite to the usual elicitation of an interaction 

 or response to denote a contact, evidence from certain mammals suggests 

 a mechanism capable of blocking a social response. Such a mechanism 



