The relation between the internal body-temperature and the respiratory movements has been worked out in hibernating dormice, hedgehogs, marmots and bats. When the temperature is below 12 deg. C., the torpid animal exhibits long periods of apnoea of several minutes' duration and interrupted by a few respirations. With the temperature rising above 13 deg. C., the periods of apnoea in the still inactive animal become shorter, the respiration suddenly commencing and ceasing (Biot's type), or gradually waxing and waning (Cheyne-Stokes' type). When the temperature is at about 16 deg. C., the periods of apnoea in the gradually awaking animal are very short and infrequent. When the temperature is about 20 deg. and rising apace, respiration becomes continuous and rapid and the animal is awake. These stages have been especially recorded in the case of dormice. In the last stage the respiration of hedgehogs and marmots is somewhat different, there being a series of rapid respirations, often followed by a single deep sighing respiration. _Respiration_ appears to be totally suspended in animals in a complete state of hibernation, if left undisturbed. It may however, be readily re-excited by the slightest stimulus; and to this fact may perhaps be attributed the belief that breathing does not actually cease. If a hibernating hedgehog be lightly touched it draws a deep breath, and breathing is maintained for a longer or shorter time before again ceasing; but if at the same time the temperature of the atmosphere be raised, respiration becomes continuous and lethargy is succeeded by activity (Marshall Hall). The opinion that respiration is totally suspended is supported by a number of facts. Hibernating marmots and bats, for example, have been known to live four hours in carbon dioxide, a gas which proves almost instantly fatal to mammals in a state of normal activity (Spallanzani). A hedgehog which may be drowned in about three minutes when awake and active, has been removed from water uninjured when in deep winter sleep after twenty-two and a half minutes' submergence. A hibernating noctule bat, when similarly treated, survived sixteen minutes' immersion. Further proof of the suspension of respiration has been furnished by experiments upon a bat which while in a deep and undisturbed state of lethargy was kept in a pneumatometer for ten hours without appreciably affecting the percentage of oxygen in the air. The same animal, when active, removed over 5 cub. in. of oxygen in the space of one hour from the instrument. As in the case of respiration, _alimentation_ and _excretion_ are suspended during hibernation.