PHILOSOPHY AS AN ORGANON 



When we come to biology, we are met by a 

 still greater complication of phenomena ; but 

 according to the luminous principle, first sug- 

 gested by Comte, that in general our means of 

 investigation increase with the complexity of 

 the phenomena, we have here an additional 

 weapon of investigation. We still retain the abil- 

 ity to experiment ; although such is the intri- 

 cacy of the circumstances, and such the subtlety 

 of the causes in operation, that we can seldom 

 apply the potent method of difference. We can 

 seldom be sure that the two instances compared 

 agree in everything save in the presence or ab- 

 sence of the circumstance we are studying. 1 In 

 experimenting upon live animals, we are liable 

 to cause a pathological state, and set in motion 

 a whole series of phenomena which obscure 

 those which we wish to observe. It is instruc- 

 tive, and often amusing, to read some treatise 

 on experimental physiology, like those of Ma- 

 gendie and Claude Bernard, and see how easy 

 it is for equally careful investigators to arrive 

 at totally irreconcilable results. It is not to be 

 denied that experiment is of vast importance 

 in biology, and has already achieved wonders. 

 Nevertheless the practical study of experimen- 

 tation should never be begun in biology, but 



1 A striking illustration of this truth is furnished by the con- 

 troversy now going on concerning archebiosis, or " spontaneous 

 generation." See below, Part II. chap. viii. 



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