THE NATURAL HISTORY OF REST 329 



the eggs is "an incidental utility that had nothing to do 

 with the nature and origin of the instinct." To find the 

 real meaning we have to go farther back, and then we see 

 that a recuperative rest naturally follows an exhausting 

 reproductive period. Far below the level of birds, long 

 before there was any incubation, we find animals resting 

 beside their laid eggs or beside their young ones. We 

 grant that this habit also afforded protection, and that it 

 may also be an expression of parental love, but the point 

 is that resting is primitive and incubation derivative. 



Even in the plant world we see the contrast between 

 the literal hard work of the vegetative period, when every 

 leaf is a busy laboratory, and the flowering and fruiting 

 period, when the activity is not in getting but in trans- 

 muting what has been already gained. And now in 

 Winter we see the leafless trees having, as it were, a deep 

 sleep. 



Let us now turn from the general conditions which make 

 rest necessary to the function of the nervous system in 

 this connection. The nervous system is very sensitive to 

 fatigue and to the poisoning of the body with accumulated 

 waste products ; one of its many functions is that of warning 

 the body when it is time to rest. But at the same time, 

 as every one knows, the nervous system is extremely 

 sensitive to stimulus ; it has in some way great resources 

 within itself ; and thus a practical antinomy often comes 

 about. The nervous system is often capable of the treason 

 of urging the body on when the weak flesh would fain rest. 

 On the one hand, it is a rest-index that automatically puts 

 on the brake ; on the other hand, it is a spur which incites 

 the tired steed to further effort. The contradict oriness of 

 these two functions is one of the difficulties of a healthy life. 

 Put in another way, the difficulty is that the human resting 

 instinct is very slightly developed, and that many find it 



