»i6 



Life and Love. 



XIII. 



PERIODIC ACTIVITY. 



ACTIVITY jti reproductive life is, like most 

 other, possibly all other, activity, periodic. 

 Periodicity seems to be a uni- 

 versal law of nature, operating 

 in every direction where motion 

 exists ; and vital motion is no 

 exception to the general rule ; 

 life, too, ebbs and flows in what 

 may be a universal rhythm. 



Physical life seems to be but a 

 mode of motion. When motion 

 ceases life ceases, — from the 

 chemical activity by which cells 

 conx'crt crude material into their 

 own living substance, to the more 

 external and visible motions of 

 the body as a whole, this essen- 

 tial fact of motion is evident. And 

 more obscurely, the periodic habit of motion is 

 also evident. 



Unseen and for the most part unsuspected, the 

 cell performs its chemical motions of combination 



