374 SCIENTIFIC THOUGHT. 



century, nor can it be stated that uniformity of opinion 

 exists even yet as to the cause of this ignorance. The 

 enormous . progress which has been made in our know- 

 ledge of the different properties of living things has had 

 an effect on the minds of those searchers to whom 

 we are mostly indebted for it, similar to that produced 

 on a wanderer who ascends an unexplored and distant 

 peak. Ever and anon, after scaling the eminence just 

 before him, he beholds a new and greater one rising 

 into view, which he contemplates with mixed feelings 

 of discouragement and of eager desire for advance. 

 But whereas our wanderer must know that the very 

 greatest height or distance is none the less a measurable 

 and attainable quantity/ what hope has the biologist to 

 encourage him on his way ? No other -as it appears 

 to some than the assurance that he is all the time ex- 

 ploring an unknown country, whereas the final achieve- 

 ment is impossible to him through the inaccessibility 

 of the position or the limitation of his own powers. 

 Others, indeed, from time to time have not taken this 

 despondent view, but, elated by the triumphs which 

 every new step has afforded them, have persistently 

 maintained that some day the last step will be taken 

 and the central peak really gained. 

 4. The history of biological thought, as distinguished 



Oscillation 



of biological from biological knowledge, presents us with the spec- 

 thought. 



tacle of a repeated oscillation between these two ex- 

 treme views : on the one side the continually recurring 

 conviction that the problem of life is insoluble, and, 

 on the other, the assertion that it is soluble, though 



