

The acquisition of oxygen by the blood in the lung 189 



the same point ; they assume a knowledge on the one hand of what 

 is simple, on the other of what is advantageous, whilst as yet the facts 

 and principles at stake are admittedly unknown. 



Let me illustrate my meaning by an analogy. It is difficult to 

 conceive of a more simple form of column than a cylinder. Yet 

 I have before my eye a hexagonal column a much more complicated 

 figure in order to be sure what it is I have to go round it, to measure 

 its angles and count its sides. This column has come from that 

 magnificent natural pile, the Giant's Causeway, in the north of 

 Ireland, where sea over sea of molten rock has shrunk and fractured 

 into a structure composed entirely of columns just similar to that at 

 which I am looking. The man who would urge the rightness of the 

 simple view may retort that his point of view is unshaken, that one 

 would be right to hold that Nature was more likely to produce a 

 cylinder than a hexagonal prism until evidence had been adduced to 

 the contrary, and that only now that I have the hexagonal prism in 

 view am I warranted in changing my mind. 



My meaning has escaped such an one. It is that the simplicity 

 of the two stones has been considered apart from their setting, apart 

 from the forces which brought them into being, and especially with 

 regard to the simplicity of those forces. Behind the complicated 

 hexagon there is a simple law of contraction, behind the simple 

 cylinder there is no simple natural process, in fact there is no natural 

 process at all it has been produced like the dialysing membrane by 

 the hand of man it might conceivably have been produced from the 

 prism by some natural process of wear and tear, as a dead membrane 

 might have been produced from a living one, which would probably 

 like a diphtheritic membrane be sloughed off" by the body. Taken 

 in its setting, the column of basalt from the Giant's Causeway is 

 the simple figure. The truth of the proposition that the simple 

 process was the more reasonable remains, but whilst the processes 

 are themselves unascertained it is impossible to be sure that the 

 process which seems the simpler does not involve consequences far 

 more complex. 



There were not wanting those who said that they could not get 

 results at all by the method pursued by Haldane and Lorrain Smith. 

 A confession of one's own weakness is not a convincing proof of some 

 one else's. 



But the cup of the diffusion theory was not yet full. Quite 

 another line of argument was adduced which, if correct, showed that 



