DEVELOPMENT BY NATURAL SELECTION. 133 



for the necessary work of digging a covered trench so 

 as to connect the downcast shaft with the fan, and thus 

 enable it to draw air from the downcast instead of the 

 upcast shaft. I followed to the pit-head three or four 

 minutes later, and was amazed to find that the helpless 

 crowd was gone. Picks and shovels had appeared as 

 if by magic, and the whole of the men were hard at 

 work along the line of the trench. In case the fan 

 did not prove powerful enough to turn the air, a message 

 was also sent through to a Yorkshire pit where there 

 was a small but very powerful fan in use for experiments ; 

 and within a few hours the Yorkshiremen had got the 

 fan on the rails, and the railwaymen had hurried it 

 through to Birmingham. 



These were the facts ; but what light can natural 

 science throw on them ? It can tell us that the actions 

 of all those concerned were bound up with endless 

 physiological processes occurring in their bodies. Audi- 

 tory or visual stimuli of different kinds started the train 

 of complicated movements which brought us together 

 at the pit-head and guided all the movements of those 

 concerned. It was again an auditory stimulus that 

 suddenly brought order and activity into the aimless 

 crowd. It was a constant supply of oxygen and oxi- 

 disable food-material properly directed by the action of 

 lungs, heart, liver, nervous system, and various other 

 organs, that made the movements possible. Had any 

 one of these factors been absent the result would have 

 been different. If, for instance, their supra-renal glands 

 had failed to respond, the brave Yorkshiremen would 

 probably have shrunk back in terror before the smoke, 

 heat, and poisonous air. At no one point can natural 



