HIBERNATION. 265 



air that remained in the cavity of the lungs becomes rarefied, 

 and forces its way out, and admits of fresh air being applied 

 to these organs."* I suspect that more of fancy than of 

 observation enters into the baronet's theory; for were the 

 rarefaction of the contained air, and its egress through the 

 pulmonary aperture, all that was necessary to shake off the 

 winter slumber, this would be done on several days in winter 

 and in early spring, when the sun shines brightly and the 

 atmospherical temperature is high enough to produce the 

 effect, often higher, indeed, than it is when they begin, in 

 the appointed time, to leave their hybernating retreats. If, 

 says M. Gaspard, individuals of Helix pomatia " were ex- 

 posed during the winter to a dry heat of from 60 to 100 

 for several days, or even weeks, not one made its appear- 

 ance ; whilst, on the contrary, those which were placed in a 

 deep recess, the regular temperature of which was 50, came 

 forth in April, or at the beginning of May, without any 

 increase of temperature." 



Dr. Turton, on the other hand, maintains that the doc- 

 trine of Gaspard is equally untenable ; for that the direct 

 communication between the external air and the animal 

 within its shell is never interrupted, but on the contrary 

 preserved, by means of a small aperture in the epiphragm. 

 His words are : " But, upon examination, it will appear, 

 that in the centre of this epiphragm (of Helix pomatia) is 

 an exceedingly minute orifice, communicating with an umbi- 

 lical cord, which is connected with a fine placenta-like tissue 

 of vessels, penetrating into the pulmonary cavity itself ; and 

 this minute orifice, although not large enough to admit a 

 drop of water, is of sufficient capacity for the passage of that 



* Comp. Anat. iii. 156. In the following extract, Sir E. Home repeats 

 his hypothesis in a more detailed manner : " It is curious that, although re- 

 spiration is necessary for carrying on the functions of life, it is by no means 

 so for the continuance of its existence. The garden-snail illustrates this 

 fact in the most satisfactory manner. When the temperature of the atmo- 

 sphere sinks below a certain degree, this animal places itself upon a solid 

 body, that it may not be liable to fall off : it then forms an operculum of 

 mucus, by which respiration is stopped, and the animal remains hermeti- 

 cally sealed up, till warmth and moisture dissolve the mucus by which the 

 animal was fixed to its place ; and a globule of air retained in the lungs, 

 which consist only of one cell or bag, being rarefied-, escapes externally, re- 

 storing the communication with the air of the atmosphere which rushes in, 

 and the action of the heart is renewed. If it is admitted that the applica- 

 tion of oxygen to the muscles of the heart is capable of stimulating that 

 organ, nothing can be more simple, than the mode in which this is effected : 

 the oxygen of the atmosphere is absorbed by the blood in the lungs, and the 

 closeness of the ventricle of the heart to the lungs, permits the oxygen to 

 penetrate to the heart." Comp. Anat. v. 129. 



