HIBERNATION AND ALLIED STATES IN ANIMALS 111 
into a condition which is related to that of hibernation. 
The so-called encysted stage of protozoa is perhaps 
analogous and similarly preservative of the individual 
and the species. 
The study of a subject like the present one gives rise 
to many questions. Can the molecular machinery of 
life entirely stop, and yet be set in motion again? We 
know that cold-blooded animals may be frozen and 
completely restored to a natural condition. This and 
the encysted condition of protozoa are suggestive of 
such a possibility. 
Yet in insects a condition of perfect quiescence is 
accompanied by the most wonderful changes. The 
worm-like caterpillar becomes within its cocoon the 
butterfly, with locomotive powers immeasurably greater. 
For myself, the more I study biological problems, the 
less am I inclined to subscribe to rigid formule of 
being. The study of a single group of animals from a 
physiological point of view, much less that of a single 
individual, does not suffice to enable one to lay down 
laws that will apply to similar processes in other groups 
of animals except in the most tentative way. I can 
never forget the lesson of my marmot that did not 
hibernate at all, and what modification of present 
views more extended study of this subject of sleep in 
all its phases will produce, it is impossible to say. 
All my own studies have greatly impressed me with 
the plasticity of living things, their power to adapt to 
altered environments, and, if I might suggest one of 
the great changes that is likely to come over the 
biology of the future, it is a recognition of the above 
fact; so that we will cease to generalise so widely 
from such narrow data, or rather, perhaps, we will be 
ready to believe that phenomena, very different from 
those we know, may be possible in the realm of living 
things. 
