the lower limbs less than that of the corresponding arteries. The same was the case with the blood of the iliac veins and arteries; that of the vena cava ascendens as far as the entrance of the renal vein was also of less temperature than that of the descending aorta below the origin of the renal arteries. The mixture of the blood of the renal vein with that returning from the lower limbs has this result, that in the vena cava comprised between the mouth of the renal vein and the liver, the blood is warmer than in the portion of the descending aorta, which extends from the diaphragm to the origin of the renal arteries; and lastly, at the point where the supra-hepatic veins disgorge their blood into the vena cava ascendens, the temperature of the blood in the last vein again rises and passes much above that of the blood of the corresponding part of the aorta. The confluence of the supra-hepatic veins and the vena cava is the warmest place in the economy. The blood, at least, has there the maximum of observed temperature.

It is not easy to account for these differences, without supposing, that each part has the power of disengaging its own heat, and that the communication of caloric from one part to another is not sufficiently ready to prevent the difference from being perceptible.

Of the mode in which heat is evolved in the system of nutrition, it is impossible for us to arrive at any satisfactory information. The result alone indicates, that the process has been accomplished. In the present state of our knowledge, we are compelled to refer it to some chemico-vital action, of the nature of which we are ignorant; but which seems to be possessed by all organized bodies,-vegetable as well as animal. We know that wherever carbon unites with oxygen to form carbonic acid; oxygen with hydrogen to form water; or with phosphorus or sulphur to form phosphoric acid, and sulphuric acid, as is constantly the case in organized bodies, heat must be disengaged.' We shall have to refer hereafter, when treating of the phenomena of DEATH, to interesting observations of Dr. Dowler of New Orleans, and others, showing, that the heat of the body may rise after somatic death, that is, after the cessation of circulation and respiration; and that the elevation of temperature varies materially in different parts of the body. The disengagement of caloric, which takes place until the supervention of the putrefactive process, must manifestly be of a physical character, and of course in no respect connected with respiration. Still, it may admit of a question, whether it be identical with that which takes place in the living body, and constitutes the function now under consideration. This much, however, the observations establish, that physical changes in the recently dead may give occasion to the evolu tion of heat in a manner strikingly analogous to what takes place during life.

It was stated early in this chapter, that man possesses the power of resisting cold as well as heat within certain limits, and of preserving his temperature greatly unmodified. A few remarks are needed in regard to the direct and indirect agents of these counteracting influences.

! Lehmann, Handbuch der physiologischen Chemie, S. 295, Leipzig, 1854.

2 See, on the whole subject of the causes of the production of heat in organized beings, Gavarret, De la Chaleur produite par les Etres Vivants, pp. 141 and 529, Paris,

As the mean temperature of the warmest regions does not exceed 85° of Fahrenheit, it is obvious that he must be constantly giving off caloric to the surrounding medium;-still, his temperature remains the same. This is effected by the mysterious agency which we have been considering, materially aided, however, by several circumstances, both intrinsic and extrinsic. The external envelope of the body is a bad conductor of caloric, and therefore protects the internal organs, to a certain extent, from the sudden influence of excessive heat or cold. But the cutaneous system of man is a much less efficient protection than that of animals. In the warm-blooded, in general, the bodies are covered with hair or feathers. The whale is destitute of hair; but, besides the protection which is afforded by the extraordinary thickness of the skin, and the stratum of fat-a bad conductor of caloric-with which the skin is lined, as the animal constantly resides in the water, it is not subjected to the same vicissitudes of temperature as land animals. Seals, bears, and walruses, which seek their food in the colder seas, sleep on land. They have a coating of hair to protect them. In the case of certain of the birds of the genus Anas, of northern regions, we meet with a singular anomaly, the whole of the circumference of the anus being devoid of feathers; but, to make amends for this deficiency, the animal has the power of secreting an oleaginous substance, with which the surface is kept constantly smeared. It may be remarked, that we do not find the quantity of feathers on the bodies of birds to be proportionate to the cold of the climates in which they reside, as is pretty universally the case regarding the quantity of hair on the mammalia.

Man is compelled to have recourse to clothing for the purpose of preventing the sudden abstraction or reception of heat. This he does by covering himself with substances that are bad conductors of caloric, and retain an atmosphere next to the surface, which is warmed by the caloric of the body. He is compelled, also, in the colder seasons, to have recourse to artificial temperature; and it will be obvious, from what has been said, that the greater the degree of activity of any organ or set of organs, the greater will be the heat developed: and in this way muscular exertion and digestion must influence its production. By an attention to all these points, and by his acquaintance with the physical laws relative to the developement and propagation of caloric, man is enabled to live amongst the Arctic snows, as well as in climates where the temperature is frequently, for a length of time, upwards of 150° lower than that of his own body. The contrivances adopted in the polar voyages, under the various discoverers, are monuments of ingenuity directed to obviate one of the greatest obstacles to prolonged existence in cold inhospitable regions, for which man is naturally incapacitated, and for which he attains the capability solely by the exercise of that superior intellect with which he has been vested by the Author of his being. In periods of intense cold, the extreme parts of the body, unless carefully protected, do not possess the necessary degree of vital action to resist congelation. In the disastrous expedition of Napoleon to Russia, the loss of the nose and ears was a common casualty; and, in Arctic voyages, frost-bites

occur in spite of every care. When the temperature of the whole body sinks to about 78° or 79°, death takes place, preceded by the symptoms of nervous depression, which have been previously detailed.

The counteracting influence exerted, when the body is exposed to a temperature greatly above the ordinary standard of the animal, is as difficult of appreciation as that by which calorification is effected. The probability is, that in such case the disengagement of heat is suspended; and that the body receives it from without by direct, but not by rapid, communication, owing to its being an imperfect conductor of caloric. Through the agency of this extraneous heat, the temperature rises a limited number of degrees; but its elevation is generally considered to be checked by the evaporation constantly taking place through the cutaneous and pulmonary transpirations. For this last idea we are indebted to Dr. Franklin,2 and its correctness and truth have been maintained by most observers. MM. Berger and Delaroche put into an oven, heated to from 120° to 140°, a frog, and one of those porous vessels called alcarazas-which permit the transudation of the fluid within them through their sides-filled with water at the temperature of the animal, and two sponges, imbibed with the same water. The temperature of the frog at the expiration of two hours, was 99°; and the other bodies continued at the same. Having substituted a rabbit for the frog, the result was identical. On the other hand, having placed animals in a warm atmosphere, so saturated with humidity that no evaporation could occur, they received the caloric by communication, and their temperature rose; whilst inert, evaporable bodies, put into a dry stove, became but slightly warmed; -much less so, indeed, than the warm-blooded animals in the moist stove. Hence, they concluded, that evaporation is a great refrigera tive agent when the body is exposed to excessive heat; and that such evaporation is considerable is shown by the loss in weight which animals sustain by the experiment. It has been contested, however, that the cutaneous evaporation has any effect in tempering the heat of the body. MM. Becquerel and Breschet3 found, when the hair of rabbits had been shaved off, and the skin covered with an impermeable coating of strong glue, suet, and resin, that the animals died soon afterwards; and, they thought, by a process of asphyxia in consequence of the transpiration from the skin being prevented. In these experi ments, to their surprise, the temperature of the animals, instead of rising, fell considerably. Thus, the temperature of the first rabbit, before it was shaved and covered with the impermeable coating, was 38° Centigrade; but immediately after the coating was dry, the temperature of the muscles of the thigh and breast had fallen to 24:5° Centigrade. In another rabbit, on which the coating was put on with more care, as soon as it was dried, the temperature was found to have fallen so much that it was only three degrees above that of the surrounding atmosphere, which was, on that day, 17° Centigrade. An hour after the animal died. These experiments-and they have been

1 Larrey, Mémoires de Chirurgie Militaire et Campagnes, tom. iv. p. 91, 106, and 123, Paris, 1817.

2 Works, iii. 294, Philad., 1809; or Sparks's edit., vi. 213, Boston, 1838.

Comptes Rendus, Oct., 1841.

repeated with like results by M. Magendie1-clearly exhibit the importance of the functions executed by the skin. Dr. Carpenter2 thinks they place in a very striking point of view the importance of the cutaneous surface as a respiratory organ, and enable us to understand how, when the aerating power of the lungs is nearly destroyed by disease, the heat of the body is kept up to its natural standard by the action of the skin. "A valuable therapeutical indication, also," he adds, "is derivable from the knowledge which we thus gain of the importance of the cutaneous respiration; for it leads us to perceive the desirableness of keeping the skin moist in those febrile diseases in which there is great heat and dryness of the surface, since aeration cannot properly take place through a dry membrane." It has been already shown,3 that local derangement of the apparatus engaged in the important functions of nutrition, calorification and secretion, is the cause of many affections which have been ascribed to a fancied check to perspiration in the part.

M. Edwards, in his experiments on the influence of physical agents on life, observed, that warm-blooded animals have less power of pro ducing heat, after they have been exposed for some time to an elevated temperature, as in summer; whilst the opposite effect occurs in winter. He instituted a series of experiments, which consisted in exposing birds to the influence of a freezing mixture, first in February, and afterwards in July and August; observing in what degree they were cooled by remaining in this situation for equal lengths of time; the result was, that the same kind of animal was cooled six or eight times as much in the summer as in the winter months. This principle he presumes to be of great importance in maintaining the regu larity of the temperature at different seasons; even more so than evaporation, the effect of which, in this respect, he thinks, has been greatly exaggerated. From several experiments on yellow hammers, made at different periods in the course of the year, it would result, that the averages of their temperature ranged progressively upwards from the depth of winter to the height of summer, within the limits of five or six degrees of Fahrenheit; and the contrary was observed in the fall of the year. Hence, M. Edwards infers, and with probability, that the temperature of man experiences a similar fluctuation."

When exposed to high atmospheric temperature, the ingenuity of man has to be as much exerted as under opposite circumstances. The clothing must be duly regulated according to physical principles, and perfect quietude be observed, so that undue activity of any of the organs, that materially influence the disengagement of animal heat, may be prevented. It is only within limits, that this refrigerating action is sufficient. At a certain degree, the transpiration is inadequate; the temperature of the animal rises, and death supervenes.

1 Gazette Médicale de Paris, 6 Déc., 1843.

Principles of Human Physiology, Amer. edit., p. 414, Philad., 1855.

3 Page 520.

De l'Influence des Agens Physiques, p. 489; and Hodgkin's and Fisher's translation, Lond., 1832.

5 See the chapter on Clothing in the author's Human Health, p. 340, Philadelphia,

VOL. I.-10

BOOK II.

ANIMAL FUNCTIONS.

THE animal functions or functions of relation comprise sensibility, and muscular motion, including expression or language. Those that are executed with consciousness are subject to intermission, constituting sleep; a condition which has, consequently, by many physiologists, been investigated under this class; but as the functions of reproduction are influenced by the same condition, the consideration of sleep will be deferred until the third class of functions has received attention.

The animal functions-as the name imports-are characteristic of the animal; and must, consequently, be accomplished by parts that appertain to it alone. They are all-in other words-attributes of a nervous system,-nothing identical with innervation existing in the vegetable.

CHAPTER I.

SENSIBILITY.

SENSIBILITY, in its general acceptation, means the property possessed by living parts of receiving impressions, whether the being exercising it has consciousness or not. To the first of the cases-in which there is consciousness-Bichat gave the epithet animal; to the second, organic; the latter being common to animals and vegetables, and presiding over the organic functions of nutrition, absorption, exhalation, secretion, &c.; the former existing only in animals, and presiding over the sensations, internal as well as external, and the intellectual and moral manifes tations.

Pursuing the plan already laid down, the study of this interesting and elevated function will be commenced, by pointing out, as far as may be necessary, the apparatus that effects it, the nervous system.

1. NERVOUS SYSTEM.

Under the name nervous system, anatomists include all those organs that are composed of nervous or pulpy tissue-neurine. In man, it is constituted of three portions: first, of what has been called the cerebrospinal or cranio-spinal axis, a central part having the form of a long cord, expanded at its superior extremity, and contained within the cavities of the cranium and spine; secondly, of cords, called nerves, in number thirty-nine pairs, according to some,-forty-two, according to others,passing laterally between the cerebro-spinal axis and every part of the body; and, lastly, of a nervous cord, situate on each side of the spine, from the head to the pelvis, forming ganglia opposite each vertebral foramen, and called the great sympathetic.