CHAPTER XI I 



RHYTHM 



RHYTmi IN PARTS OF CELLS— RHYTHM IN C1<:LLS— RHYTHM 

 IN TISSUES— RHYTHM IN ORGANS— RHYTHM IN ORGANISMS 



—RHYTHM IN COMMUNITIES 



So do flux and reflux — the rhythm of change — alternate and 

 persist in everything under the sky. 



Thomas Habdy, less of ihe D'Urberuilles. 



We have said in Chapter I that one of the characteristics 

 of Hving matter is rhythm: in fact, the whole of Nature sliows 

 certain rhythms. Summer and winter, seed-time and harvest, 

 night and day, follow one another at regular intervals. In 

 the sonorous words of Addison : 



Th' unwearied Sun from day to day 

 Does his Creator's power display. 



• • • « • • • 



Soon as the evening shades prevail 

 The Moon takes up the wondrous tale, 

 And nightly to the listening earth 

 Repeats the story of her birth. 



These external influences have their effect on both plants 

 and animals, and are responsible for many of their rhythms. 

 But apart from external stimuli there is an innate rhythm in 

 living matter. 



Rhythm in Parts of Cells 



Parts of cells may have rhythm. The contractile vacuoles 

 of the Infusoria contract at intervals which are sometimes 

 regular and sometimes irregular. There seems to be a great 

 deal of variation in the rate of contraction of the vacuoles 

 in different individuals, in the same individual at different 

 times, and in the two vacuoles in the same individual. 



The times between successive contractions of the vacuoles 

 o£ Pararnoeciiim were observed and found to vary from 15 sees, 

 to 40 sees, with an average of 27-5 sees. In one case where tiie 

 two vacuoles in the same individual were observed it was 



