8 Animal Life and Intelligence, 



its head under its wing and goes to sleep. The cattle in 

 the meadows, the sheep in the pastures, the horses in the 

 stables, the birds in the groves, all show alternating periods 

 of activity and repose. But is this true of all animals ? 

 Do all animals " move about and sleep " ? The sedentary 

 oyster does not move about from place to place ; the 

 barnacle and the coral polyp are fixed for the greater part 

 of life ; and whether these animals sleep or not it is very 

 difficult to say. We must make our statement more com- 

 prehensive and more accurate. 



If we throw it into the following form, it will be more 

 satisfactory : Animals exhibit certain activities ; and 

 periods of activity alternate with periods of repose. 



I shall have more to say hereafter concerning the 

 activities of animals. Here I shall only say a few words 

 concerning the alternating periods of repose. No organism 

 can continue in ceaseless activity unbroken by any inter- 

 vening periods of rest. Nor can the organs within an 

 organism, however continuous their activity may appear, 

 work on indefinitely and unrestfully. The heart is appa- 

 rently restless in its activity. But in every five minutes 

 of the continued action of the great force-pump (ventricle) 

 of the heart, two only are occupied in the efforts of con- 

 traction and work, while three are devoted to relaxation 

 and repose. What we call sleep may be regarded as the 

 repose of the higher brain-centres after the activity of the 

 day's work — a repose in which the voluntary muscles share. 



The necessity for rest and repose will be readily under- 

 stood. We have seen that the organism is a centre of 

 waste and repair, of nicely balanced destructive and recon- 

 structive processes. Now, activity is accompanied by 

 waste and destruction. But it is clear that these processes, 

 by which the substance of the body and its organs is used 

 up, cannot go on for an indefinite period. There must 

 intervene periods of reconstruction and recuperation. 

 Hence the necessity of rest and repose alternating with 

 the periods of more or less prolonged activity. 



7. They feel — '' at least some of them do,'\ The quali- 



