78 
FIRST CLASS OF THE VERTEBRATED ANIMALS. 
As the stomach is a muscular organ, and as the passage of the food through the 
pylorus depends upon the rapidity with which the almost insensible contractions of the 
Stomach are performed, it follows that Sleep retards digestion, while, at the same 
time, it renders it more complete. This slowness of digestion is further increased by 
the sUte of rest in which the body remains, as nothing tends more to excite a rapid 
digestion than the gentle motion of the limbs, or of the entire body. The same 
phenomena take place in the intestines, where the aliments remain ahnost inert in 
the several portions of the alimentary canal. However, the slowness of this movement 
favors the formation of chyle, and renders its absorption more compleU. 
Absorption is very active during Sleep, and the danger of slumbering in noxious 
air hence becomes very great. Travellers are usually advised to avoid sleeping in 
marshy situations, such as the Pontine Marshes of Italy, especially in the warm sea- 
son of the year. Perspiration also is performed more easily, because the pores remain 
open during the state of muscular relaxation. “ 0ne nutrition plus efficace, la re- 
paration graduelle des forces qui cn resulte, et aussi la replkion de la vessie, toutes 
ces choses reveiUent en nous, durant le sommeil, des idees de jouissance et des sou- 
venirs de volupte. 
As all the senses do not fall asleep at the same time, so they differ in the order in 
which they awake. Taste and Smell commonly resume their functions last of all. 
The sense of Sight is roused with greater difficulty than that of Hearing. An un- 
expected noise will often awaken a Somnambulist from his lethargy, upon whom the 
strongest rays of light will have had no previous effect, although his eyes continue 
open. Touch, as it was the last sense to become dormant, so it appears to be the 
most easily roused. The same person who cannot be awakened by very loud 
noises, will rise instantly on being gently tickled on the soles of the feet. Often the 
mere approach of the respiration of another will be sufficient to rouse the soundest 
sleeper. 
The positions which the Mammalia assume during .Sleep are very various. The 
young animal sleeps with its limbs gathered together, in a posture most resembling 
that of the foetus in the womb. This situation is very favorable to the renewal of 
the animal forces, by permitting the relaxation of all the articulations, and in preserving 
the heat of the more sensitive parts. For the latter reason, the Dog and Cat sleep 
with their bodies forraad into a circle. Some Mammalia sleep in the open air, while 
others retire to caves and sheltered places. Many repose without any covering, 
while others prepare a bed of sonte imperfectly-conducting substance, to preserve the 
temperature of their bodies, which would otherwise fall during Sleep below the na- 
tural standard. It is usually on the right side that Man reposes. This posture 
favors the action both of the heart and stomach, as the vibrations of the former 
would reverberate through the body from the reaction of the substance upon which 
it reposes, and the latter would be compressed by the weight of the liver. After 
sleep, all the organs, being refreshed, repaired, and completely nourished, acquire a 
greater size ; thus Man and other animals which commonly hold the spine more or 
less erect, are taller in the rooming than in the evening after the fatigues of the 
day. 
Sleep is not always profound ; some of the animal functions continue to act ; ideas 
succeed each other, and the animal is said to dream. The power of dreaming is 
falsely ascribed to Man alone ; other Mammalia dream likewise, because they are 
capable of thought, and possets a certain degree of intelligence. Sometimes the Dog 
is observed to howl, struggle, and perspire copiously. Moving his tail and limbs 
rapidly, be pursues the Hare in imagination, and, on the point of seizing it, closes his 
teeth and lips as if in the act of dyeing them in blood. Some Birds are also known 
to dream, as the Parrots. Those animals which are most easily excited dream more 
frequently than the others;. thus the Horse is more liable to dream than the Bull. 
According to Chabert, this phenomenon among Cattle is observed only in the Bull, 
the Ram, or in Cows which are suckling. 
It is possible to protract the usual period of sleep by an unusual excitement ; but if 
the stimulus be long conlinned its effect goes off, and then nothing can prevent sleep ■ 
as long as the health continues good. In fact, sleep, once in the twenty-four hours, 
is as essential to the existence of the Mammalia as the momentary respiration of fresh 
air. The most unfavorable conditions for - sleep cannot prevent its approach. 
Coachmen slumber on their coaches and couriers on their horses, while soldiers fall 
asleep on the field of battle, amidst all the noi.se of artillery and the tumult of war. 
During the retreat of Sir John Moore, several of the British soldiers were reported 
to have fallen asleep upon the march, and yet they continued walking onwards. The 
most violent passions and excitement of the mind cannot preserve even powerful 
minds from sleep; thus Alexander .the Great slept on the field of Arhcla, and Napo- 
leon upon that of Austorlitz. Even stripes and torture cannot keep off sleep, as cri. 
minals have been known to slumber on the rack. Noises which serve at first to drive 
away sleep, soon become indispensable to its existence ; thus a stage-coach stopping 
to change horses, wakes all the passengers. The proprietor of an iron forge, who 
slept close to the din of hammers, forges, and blast furnaces, would awake if there 
w<as any interruption to them during ilie night ; and a sick miller, who had his mill 
stopped on this account, passed sleepless nights until the mill resumed its usual 
noise. Homer, in the Iliad, elegantly represents sleep as overcoming all men, and 
even the gods, excepting Jupiter alone. 
The length of time passed ia sleep is not the same for all men ; it varies in dif* 
ferent individuals and at different ages ; but nothing can be determined from the time 
past in sleep, relative to the strength or energy of the functions of the body or mind. 
From six to nine hours is the average proportion, yet the Roman Emperor Caligula 
slept only three hours. Frederic of Prussia and Dr John Hunter consumed only 
four or five hours in repose ; while the great Scipio slept daring eight. A rich and 
lazy citizen will slumber from ten to twelve hours daily. It is during mfaney that 
sleep is longest and most profound. Women also sleep longer than men, and young 
men longer than old. Sleep is driven away during convalescence after a long sick- 
ness, by a continued fasting, and the abuse of coffee. The sleepless nights of old 
age are almost proverbial. It would appear that carnivorous animals sleep in gene- 
ral longer than the herbivorous, as the sup.'rior activity of the muscles and senses of 
the former seem more especially to require repair. Satiated with their prey, they 
are obliged to seek repose to digest those very substantml matters which compo&e 
their aliment. 
In general, it may be stated, that during sleep the internal functions predominate 
over those relating to the exterior of the body. Every thing which tends to inter- 
rupt the relations of the external with surrounding objects serves to induce sleep. 
On the contrary, the existence of external .stimuli tend to expel it, until at length 
they lose their effect by long-continued exorcise. 
From this it ought to follow that excessive cold, which benumbs the external 
powers, ought to occasion sleep. When exposed to the action of a low temperature, 
animals experience an irresistible desire to sleep, which soon terminates in death. 
Of this there are frequent examples in the inhospitable climates of the north, Sibe- 
ria, Lapland, and Karaschatka, or on the tops of high mountains, as the glaciers of 
Switzerland. Dr Solander and party nearly lost their - lives from this cause among 
the hills of Terra del Fuego. Surprised by an excessive cold, he was with difficulty 
prevented by his companions from yielding to this impulse of nature, although know- 
ing well the consequences of sleeping. — (See Captain Cook's First Voyage). Tra- 
vellers on horseback are peculiarly liable to be overcome by this propensity to sleep, 
when the cold is very intense, in which case they are sure to be frozen to death. 
There prevails among many ISlamraalia a singular internal modification, which can- 
not be explained by any cause more general than itself, but must be referred to some 
unknown original constitution. We refer to that state of torpidity commonly called 
Hybernation, into which some animals fall during a part of the autumn and in win- 
ter, but from which they escape early in spring. Although we are wholly ignorant 
of the cause of this winter sleep, the effects and design arc well known. It seems 
obviously intended to preserve the animals in situations where they could not have 
maintained their existence, from the impossibility of finding an adequate supply of 
food. Accordingly, all the active functions of life are suspended, where their exor- 
cise would be incompatible with more general laws. 
At a more or less advanced period of the autumn, depending on the degree in 
which the temperature is lowered, animals possessed of this peculiar constitution seek 
to shelter themselves from the cold and wind, by retiring into holes excavated in the 
ground, walls, trees, or among the bushes. These retreats they line carefully with 
grass, green loaves, moss, and other bad conductors of heat. Hybemation occurs 
among several of the Mammalia, as in the Fat Dormouse (^Myoxus gVts), the Garden 
Dormouse (il/. nitela), the Common Dormouse (Af. afc/Zunarms), the Hedgehog 
(^Erinaceus Europems), the Bats, the Alpine Marmot mamoin), the 
Hamster (^Cricetus vulgaris), the .Tumping Mouse of Canada (hlcriones nemoralis), ■ 
and some others. Animals with cold blood hybornate as well as some of the Mam- 
malia. Many Reptiles become torpid in cold climates, as well as some Insects, Mol- 
luscs, and Wormi ; but in general the degree of their lethargy is much less profound 
than that of the hybernating Mammalia. They pass their time of hybernation with- 
out food, but are not always deprived of sensation and motion, even at the freezing 
point. 
“ It is highly important,” observes Dr Marshall Hall, “ to distinguish that kind 
of torpor which may be produced by cold in any animal from true hybernation, which 
ia a property peculiar to a few species. The former is attended by a benumbed state of 
the sentient nerves, and a stiffened condition of the muscles ; it is the direct and im- 
mediate effect of cold, and even in the hybernating animal is of an injurious and fatal 
tendency ; in the latter, the sensibility and motility arc unimpaired, the phenomena 
are produced through the medium of sleep, and the effect and object are the preser- 
vation of life. Striking as these differences are, it is certain that the distinction has 
not always been made. In all the experiments which have been made with artificial 
totnneratures especially, it is obvious that this distinction has been neglected. True 
hvbernation is induced by temperatures only moderately low. All hybernating ani- 
mals avoid exposure to extreme cold. They seek some secure retreat, make 
themselves nests or burrows, or congregate in clusters ; and if the season prove un- 
usually severe, or if their retreat bo not well chosen, and they be exposed, in conse- 
quence, 10 excessive cold, many become benumbed, stiffen, and die. To induce true 
hybernation it is quite necessary to avoid extreme cold, otherwise we produce the 
benumbed and stiffened condition to which the true torpor or torpidity may be ap- 
propriated. I have even observed that methods which secure moderation in temper- 
ature lead to hybernation. Hedgehogs supplied with hay or straw, and Dormice 
supplied with cotton wool, make themselves nests, and become lethargic ; when others, 
to which these materials are denied, and which are consequently more exposed to cold, 
remain in a state of activity. In these cases warmth, or moderate cold, actually con- 
cur to produce hybernation. 
The kind of retreat which each animal prepares varies with the species. The 
Bats, besides hybernating in holes, also hang suspended in grottoes and caverns, 
where the temperature is milder than in the open air. Other hybernating animals 
are satisfied with bringing their head nearer to their lower extremities, so as to p*'®' 
sent a surface of leas extent to the cold. On discovering them in their retreats, 
they are found rolled up, cold to the touch, motionless, stiff, their eyes closed, their 
respiration slow, interrupted, scarcely perceptible, or none at all. Their insensibility 
is sometimes such that they may be moved, rolled about, and shaken in every possible 
way, without being disturbed from their torpor. 
During the spring or summer, when these animals enjoy their full activity, they 
possess an elevated temperature, which may vary according to the species and indi- 
viduals, between and 98^” Fahrenheit, and consequently is between those limit* 
which characterize the animals with warm blood. When examined in the autumn, 
with the view of ascertaining the changes which- they then undergo, it is observe 
that their tcniperaturo falls rapidly as the cold season advances. Their respiration 
gradually becomes impeded, their movements are less rapid, and their appetite di 
minishes ; but these animals stiD maintain the use of their senses and the power o 
locomotion. This intennediate state, between the full possession of life in all its vi- 
gour, and absolute torpidity, may continue for one or two months. 
The degree of external temperature at which they become absolutely torpid rs" 
rios with the species, and even according to the individual. In general, the dispo»‘' 
tion to hyhernate follows in a descending scale of temperature, of which the follow- 
