MIDWINTER 129 
as well as retrospective reference; it is the crouch 
before the leap. Many an organism has learned 
the lesson, se reculer pour mieux sauter. The 
repose of winter gives us the rebound of spring. 
On the moor a few hundred feet lower down there 
are scattered birch trees with bare limp branches 
on the pendulous tips of which the sun has hung 
diamonds; what a story they have to tell us of 
the precarious tenure of peripheral organs (as the 
birch leaves fell the grouse molted its claws!); of 
the usefulness of surrendering vulnerable organs; 
of the economy of the organism, for the leaves in 
their withering gave back to the tree all that they 
had that was worth keeping; and of the prepara- 
tions made many months ago within the well- 
protected buds for the foliage and flowers of the 
distant spring. 
From the external aspect the big fact is that the 
rate of chemical reactions is increased by rise of 
temperature, since that means increase in the rate 
of molecular movements. It is true that what is 
called van Hoff’s Law of the effect of temperature 
on chemical reactions does not seem to fit very 
well for the changes that go on in living creatures, 
probably because these are such heterogeneous 
systems, in which physical and chemical processes 
become intricately mixed up; but the broad fact 
is that the effect of warmth is to increase, and the 
effect of cold to decrease, the rate of vital activity 
or metabolism. Moreover, in spite of glacier-fleas 
and small creatures from hot springs, the great 
