64 WESLEY MILLS ON 



All forms ol' prol'ouud wiuter (or summer) sleep are protective, both of the individual 

 and the species. Manifestly amphibia, reptilia and other groups of the animal kingdom 

 must have utterly vanished from the face of the earth but for such a power to adapt to 

 conditions. Probably manj^ individuals, if not some entire groups have through more or 

 less complete failure to adapt disappeared before this habit of the nervous system and 

 of the whole organism became perfect enough. 



It is equally clear from the investigation given to the subject that hibernation, like 

 daily sleep, is not a fixed and rigid thing, but just as it has been the result of adaptation 

 to the environment by virtue of the plasticity of function of all living cells, so the power 

 to modify, still remains. 



It is possible to conceive of its being lost in certain groups of animals ; indeed this 

 phase of the subject has been as much impressed on me as the other. Sleep, hibernation 

 and all such states are not invariable but to a certain extent so dependent on the sur- 

 roundings that, as in the case of my last marmot, also of turtles and frogs kept within 

 doors, there may be an omission of that condition which is habitual under the normal 

 environment of the animal. 



I w^ould like to emphasize these facts, for they seem to me to throw great light on the 

 evolution of function at all events, and on those changes which may become so great as to 

 lead, we can hardly say, to what, in the lapse of time. 



For years I have had turtles and especially frogs under observation during the win- 

 ter months. Our frogs for laboratory use at McGill University are kept in a tank in 

 which the water is being continually renewed by a slow stream. They are not fed. None 

 of the frogs seem to pass into a condition of true hibernation, but ihey descend to the 

 bottom of the tank and remain quiet as if asleep or partially torpid, as indeed I know 

 they often are for hours. In this is an interesting modification of that most profound 

 torpor which they experience when buried in the mud of ponds. 



Even in the winter life of a creature like the marmot we may have all degrees of 

 drowsiness or torpor as I have shown ; and it is not to be forgotten that our own daily 

 sleep has its degrees, so that the night's sleep may be represented by a curve with a sharp 

 rise and^very gradual fall ; which may, as we all know, be greatly modified by circum- 

 stances. 



The same laws seem to apply to all the known cases of human lethargy, hibernation, 

 sleep or whatever the state may be called. In the case of the buried sheep and hogs the 

 protective value of the condition is evident, as also in the case of the lethargic woman. 

 This individual with so ill-balanced and unstable a constitution would probably have 

 been carried ofl' Ytj some form of actual disease long before, had she remained awake. 

 She could exist as a mere vegetative organism, but not as a normal human being in the 

 ordinary struggle for existence. One thing Avhich has been much impressed upon me by 

 my studies of this whole subject is the varying degrees of sensitiveness to temperature 

 and meteorological conditions in different groups of animals and different individuals of 

 the same group. The bat as compared with the marmot, for example, may be worked like 

 a machine by varying the temperature. On the contrary the degree to which the wood- 

 chixck is independent of temperature was a surprise to me after my experience with the 

 bat. But the woodchuck answered like a barometer to predict storms ; in fact I am satis- 

 fied that many wild animals have a delicate perception of meteorological conditions which 



