Spallanzani placed a marmot in carbonic acid gas, and makes the following report of the ex periment in a letter to Senebier: " Vous vous rcssouviendrez de ma marmotte qui fut si forte men( lethargique dans l'hiver sev•e de 1795 ; je Ia tins alors pendant quatre heures dans le gaz acide carbonique, le thermom2.tre marquant elle continua de vivre dans ce gaz qui est he plus mortel de tous, comme je vous he disais : au moins un rat ct un oiseau que j'y plasai avec elle y perirent a Einstant meme. II parait done rine sa respiration fut suspcndue pendant tout ce tems-la. Je soumis a Ia meme experience des chauve-souris semblablement lethargiques, et he resultat fut he meine." I A bat which was lethargic in an atmosphere of 36° was immersed in water of 41°. It moved about a little, and expelled bubbles of air from its lungs. It was kept in the water during six teen minutes, and then removed. It appeared to be uninjured by the experiment.
A hedgehog which had been so lethargic in an atmosphere of 40° as not to awake for food during several days, was immersed in water of 42°. It moved about and expelled air from its lungs. It was retained under the water during 221 minutes. It was then removed. It ap peared uninjured.
It seems probable that the motions observed in these animals were excited through the me dium of the cutaneous nerves.
The power of supporting the abstraction of oxygen gas, or atmospheric air, belongs solely to the hibernating state, and is no property of the hibernating animal in its state of activity. After having found that the dormant bat, in summer, supported immersion in water during eleven minutes, uninjured, I was anxious to know whether the active hedgehog possessed the same power. I immersed one of these ani mals in water. It expired in three minutes, the period in which immersion proves fatal to the other mammalia. Sir Anthony Carlisle has, therefore, committed an error, somewhat similar to that of M. Edwards, when he asserts that " animals of the class Mammalia, which hibernate and become torpid in winter, have at all times a power of subsisting under a confined respiration, which would destroy other animals not having this peculiar habit."' The power of bearing a suspended respiration is an in duced state. It depends upon sleep or lethargy themselves, and their effect in impairing or sus pending respiration ; and upon the peculiar power of the left side of the heart, of becoming veno-contractile under these circumstances.
The circulation is reduced to an extreme de gree of slowness, according to a law well known, but hitherto, I believe, unexplained, according to which the respiration and the cir culation are always proportionate to each other.
The wing of the bat aflords an admirable op portunity of observing the condition of the cir culation during hibernation. But it requires peculiar management. If the animal be taken from its cage, and the wing extended under the microscope, it is roused by the operation, and its respiratory and other movements are so ex cited, that all accurate observation of the condi tion of the circulation in the minute vessels is completely frustrated. Still greater caution is required in this case than even in the observa tion of the respiration and temperature.
After some fruitless trials, I at length suc ceeded perfectly in obtaining a view of the mi nute circulation undisturbed. Having placed the animal in its state of hibernation, in a little box of mahogany, I gently drew out its wing through a crevice made in the side of the box; I fixed the tip of the extended wing between portions of cork ; I then attached the box and the cork to a piece of plate-glass; and lastly, I left the animal in this situation, in a cold atmo sphere, to resume its lethargy. (See fig. 306.) I could now quietly convey the animal ready prepared, and place it in the field of the micro scrope without disturbing its slumbers, and observe the condition of the circulation.
In this manner I have ascertained that, although the respiration be suspended, the cir culation continues uninterruptedly. It is slow in the minute arteries and veins ; the beat of the heart is regular, and generally about twenty eight times in the minute.
We might be disposed to view the condition of the circulation in the state of hibernation as being reptile, or analogous to that of the batra cluan tribes. But when we reflect that the re spiration is nearly, if not totally, suspended, and that the blood is venous,* we must view the condition of the circulation as in a lower conditinn still, and, as it were, sub-reptile. It may, indeed, be rather compared to that state of the circulation which is observed in the frog from which the brain and spinal marrow have been removed by minute portions at distant inter vals.t In fact, in the midst of a suspended respira tion, and an impaired condition of some other functions, one vital property is augmented. This is the irritability, and especially the irrita bility of the left side of the heart. The left side of the heart, which is, in the hibernating animal, in its state of activity, as in all the other mammalia, only arterio-contraetile, be comes veno-contractile.