268 THE SOCIAL LIFE OF ANIMALS 



inhibiting influence which prevents other nymphs 

 from becoming soldiers. In the normal course of 

 events a second soldier appears only when the colony 

 has become sufficiently numerous so that the soldier- 

 inhibiting substance is spread among so many that 

 the effect on any one nymph is weakened; and some- 

 thing of the same effect of numbers may explain 

 why, in a large colony, many nymphs develop at 

 times into sexually mature and winged forms. 



There seems to be a relation to the more gen- 

 eralized situation noted earlier. When many animals 

 are exposed together to a given amount of alcohol 

 or some other toxic material, no one of the many 

 may receive any overdose, as will certainly happen 

 when one or a few individuals meet the full effect 

 of the poison. This type of relatively simple mass 

 effect, first discovered in experiments on group phys- 

 iology among animals that at the most are only 

 partially socialized, apparently turns out to be an 

 important mechanism in regulating caste formation 

 among these highly social termites; and some simi- 

 lar mechanism may control the activity of worker 

 bees in producing new queens. It is true that the 

 control of caste production is probably not the 

 simplest form of physiological mass action, for the 

 insects may from time to time become less sensitive 

 to such inhibition. At these times, many of the 



