598 THE POPULAR SCIENCE MONTHLY. 



simply as changes, must not be regarded as peculiar, and fundament- 

 ally unlike the changes of inorganic matter. 



Vital changes cannot, however, be regarded as changes simply 

 standing by themselves, for, if we overlook their adjustment to the 

 accomplishment of a purpose, we omit their most essential character- 

 istic. 



In so far as the contraction of a muscle is simply a change, it is 

 without doubt purely physical ; but in the adjustment of this change 

 to a relation between external changes, in its adaptation to a purpose, 

 we have something which has no parallel except in living things, and 

 perhaps some of man's contrivances, such as the automatic governor 

 of the steam-engine. Living things are distinguished from those 

 which have not life by their adjustment, and life consists in this ad- 

 justment. Small as this difference seems when stated abstractly, 

 and unimportant as it appears to be when we contrast such an organ- 

 ism as an amoeba, with its simple and almost mechanical power of 

 retracting its pseudopodia upon irritation, and such a highly-com- 

 plex and changeable inorganic being as the ocean, yet, considered not 

 in itself but in its adjustment to external relations, this power in the 

 amoeba separates it very widely from all inorganic forms of existence, 

 and connects it with the highest manifestations of life ; for the series 

 of adjustments of which that of the amoeba is one of the simplest may 

 be traced almost without break up to the most rational actions of 

 man. A vorticella contracts and folds down its circlet of cilia when 

 touched, because there is a connection between violent contact and the 

 presence of danger ; and this recognition of a connection between the 

 changes of the external world is knowledge of the order of Nature, and 

 this, in its higher form, is experience, and experience implies memory, 

 and memory and experience are forms of consciousness. Thus we 

 are able to understand the meaning of such expressions as that of 

 Haeckel, that living things are distinguished from the not living by 

 the possession of memory. It seems best to restrict the use of such 

 purely subjective terras as memory and experience to the higher 

 forms of conscious life, but we must not overlook the fact that the 

 existence of an adjustment between internal and external relations 

 implies something fundamentally like the memory of higher animals. 



Finally, I wish to call attention to the fact that natural selection 

 is constantly acting through the law of the survival of the fittest, in 

 such a way as to bring each organism into more and moi'e perfect 

 harmony with its environment ; that is, it is constantly bringing about 

 a more and more exact, definite, and perfect adjustment betw^een ex- 

 ternal and internal relations. If this adjustment constitutes vitality, 

 and if natural selection furnishes an explanation of the manner in 

 Avhich the adjustment has been brought about, have we not, in the 

 laAV ,of natural selection, an explanation of the origin of life ? not 

 of course of the origin of the matter of life, nor of the changes of 



