1

the parts to which they are usually referred, attract our attention to them principally, in consequence of the sensation which accompanies them being there chiefly experienced. The same may be said of the different gestures that accompany the various emotions. They are dependent upon the influence exerted by the function of sensibility on the other functions. Gall,' in his system, has feebly attempted to show, that each gesture has a reference to the encephalic situation of the organ concerned in the production of the emotion of which it is a concomitant. The idea was suggested to him, he asserts, by the fact, observed by him a thousand times, that in fractures of the skull, the hand, (naturally we should think,) was carried mechanically to the seat of the fracture. He farther remarks, that the organs of the memory of words and of meditation are seated in the forehead; and that the hand is carried thither, whenever we are engaged in deep study;-that the organ of religious instinct corresponds to the vertex; and hence, in the act of prayer, all the gestures are directed towards that part of the body. Like every professed systematist, Gall is here pushing his principles ad absurdum. They are, indeed, controverted by facts. The hand is usually carried, not to the part of the encephalon in which any passion is effected, but to the part of the body in which its more prominent effects are perceptible,-as to the region of the stomach or heart; and frequently the gesture is referable to the determinate action, which must be regarded as a necessary effect of the passion.

Finally, poetry and painting belong properly to the varieties of expression; but they are topics that do not admit of elucidation by physiology.

Here terminates the history of the animal functions, which have the common character of being periodically suspended by sleep. By many physiologists, this function has, therefore, been examined in this place; but as the nutritive and generative functions are, likewise, greatly influenced by sleep, we shall follow the example of M. Magendie, and defer its study until those functions have been inquired into.

CILIARY MOTION.

Although not an animal function, it may be convenient to allude, in this place, to the phenomena of vibratory or ciliary motion, which, in recent times, have received the attention of observers. These terms have been employed to express the appearance produced by cilia,—a peculiar sort of moving bodies resembling small hairs, which are visible by the aid of the microscope, on parts that are covered with ciliary or vibratory epithelium.3

1 Sur les Fonctions du Cerveau, v. 436, Paris, 1825.

Précis Elémentaire, i. 366.

See page 132; and, also, Sharpey, art. Cilia, Cyclop. of Anat. and Physiol., P. vi., p. 606, Lond., 1836; and Henle, Allgem. Anat., or Jourdan's French Translation, p. 251, Paris, 1843; and the excellent article Flimmerbewegung, by Valentin, in Wagner's Handwörterbuch der Physiologie, 3te Lieferung, s. 484, Braunschweig, 1842.

Fig. 208.

This ciliary motion has been seen in different animals, on the external surface, in the alimentary canal, the respiratory system, the female generative organs; and in the cavities of the nervous system. It has not been observed, however, in the vagina; but may be traced from the lips of the os uteri through its cavity, and through the Fallopian tubes to their fimbriated extremities. In the upper classes of animals, it is not witnessed on the external surface except in the embryo. In most animals, a high magnifying power is necessary to perceive it. A small piece of mucous membrane, on which it exists, should be moistened with water, and covered with a plate of glass, by which the membrane is spread out, and its border rendered clearly visible. With the aid of a powerful microscope, an appearance of undulation is perceptible, and small bodies floating in the water may be seen, near the border of the membrane, to be driven along in a determinate direction. With a still higher magnifying power, the cilia themselves may sometimes be recognized, although seldom very distinctly, owing to the great rapidity of their motion. The influence of the motion on the fluids and small bodies in contact with the membrane may be well exhibited by strewing a fine powder on the surface; as the motion of the cilia has a uniform direction, it gives rise to currents over the surface of the membrane.

1. Portion of a bar of the gill of the Mytilis eduepithelium particles from frog's mouth. 3. Ciliated epithelium particle from inner surface of human membrana tympani. 4. Ditto, ditto: from the human bronchial mucous membrane. 5. Leucophrys patula, a polygastric infusory animalcule; to show its surface covered with cilia, and the mouth surrounded by them. (Todd and Bowman.)

lis, showing cilia at rest and in motion. 2. Ciliated

Vibratile or Ciliated Epithelium.

a. Nucleated cells, resting on their smaller extre..mities. b. Cilia.

An easy mode of observing the phenomenon is to scrape with a knife a few scales of epithelium from the back of the throat of a living frog. If these be moistened with water or serum, they will continue to exhibit the motion of the adherent cilia for a very considerable time, if the epithelium be only kept moistened. On one occasion, Messrs. Todd and Bowman observed a piece of epithelium prepared in this manner exhibit motion for seventeen hours; and they thought it would probably have done so for a longer time had not the moisture around it evaporated. In the turtle, after death by decapitation, MM. Purkinje and Valentin found it lasted in the mouth nine days; in the trachea and lung, thirteen days; and in the oesophagus, nineteen days.1

Physiological Anatomy and Physiology of Man, by Messrs. Todd and Bowman, p. 62, Lond., 1843.

2

According to M. Donné,1 cilia are seen only on the "true mucous membranes" of his division, or those that secrete an alkaline mucus. They are never met with on the acid membranes, which are analogous to the skin, and simple reflections of the cutaneous envelope. Hence, they are not found in the mouth or vagina, but in the nasal and bronchial mucous membrane.

The organs of ciliary motion are delicate transparent filaments, varying in length, according to Purkinje and Valentin, from 7 to To of an inch, and are generally thicker at the base than at the free extremity. Their motion continues after death as long as the tissues retain their contractility, and often much longer. Müller3 thus sums up the present state of our knowledge in regard to the phenomenon: That the ciliary motion of the mucous membranes is due to the action of some unknown contractile tissue, which lies either in the substance of the cilia or at their base,-that this tissue resembles in contractility the muscular and other contractile tissues of animals;-that its properties so far agree with those of the muscular tissues-at all events with those of the involuntary muscles of the heart, and the vibratory laminæ of the lower crustacea;-that the motions, which it produces, continue without ceasing with an equable rhythm ;-that its properties agree also with those of the muscular tissue of the heart in its motions, continuing long after the separation of the part from the rest of the animal body;-that this tissue differs essentially, however, from muscle, in the circumstance of its motions not being arrested by the local application of narcotics; and lastly, that the ciliary motion presents itself under conditions where it is not probable that a complicated organization exists,—namely, in the undeveloped embryos of polypiferous animals.

M. Donné regards the cilia as animalcules; resembling in many. respects the spermatozoids. They certainly resemble each other; but there is no sufficient reason to believe either of them animalcular.

The production of currents by the ciliary motion is not easy of explanation. Purkinje and Valentin ascribe them to the return of the cilia from the bent to the erect state, which gives an impulse to the fluid. The direction in which the cilia act is most commonly towards the outlet of the canal on which they are placed; but, as Mr. Pagets has remarked, their special purpose is in many instances-for example, in the ventricles of the brain-as uncertain as the power by which they

act.

We shall have to refer to ciliary motion under other heads.

1 Cours de Microscopie, p. 170, Paris, 1844.

2 See Secretion of Mucus in vol. ii. of this work.

3 Elements of Physiology, by Baly, P. iv. p. 866, Lond., 1838.

Op. cit., p. 176.

Brit. and For. Med. Review, July, 1842,

p. 264.

BOOK II.

NUTRITIVE FUNCTIONS.

THE human body, from the moment of its formation to the cessation of existence, is undergoing constant decay and renovation-decomposition and composition:-so that at no two periods can it be said to have exactly the same constituents. The class of functions about to engage attention, embraces those that are concerned in effecting such changes. They are seven in number;-digestion, by which the food, received into the stomach, undergoes such conversion as fits it for the separation of its nutritious and excrementitious portions; absorption, by which this nutritious portion, as well as other matters, is conveyed into the mass of blood; respiration, by which the products of absorption and venous blood are converted into arterial blood; circulation, by which the vital fluid is distributed to every part of the system; nutrition, by which the intimate changes of composition and decomposition are accomplished; calorification, by which the system is enabled to resist the effects of greatly elevated or depressed atmospheric temperature, and to exist in the burning regions within the tropics, or amidst the arctic snows; and secretion, by which various fluids and solids are separated from the blood;-some to serve useful purposes in the animal economy; others to be rejected from the body.

CHAPTER I.

OF DIGESTION.

THE food, necessary for animal nutrition, is rarely found in such a condition as to be adapted for absorption. It has, therefore, to be subjected to various actions in the digestive organs; the object of which is to enable the nutritive matter to be separated from it. These actions constitute the function of digestion; in the investigation of which we shall commence with a brief description of the organs concerned in it. These are numerous, and of a somewhat complicated

nature.

1. ANATOMY OF THE DIGESTIVE ORGANS.

The human digestive organs consist of a long canal, varying considerably in its dimensions in different parts, and communicating externally by two outlets,-the mouth and anus. It is usually divided into four chief portions-the mouth, pharynx, œsophagus, stomach, and intestines. These we shall describe in succession.

1. The mouth is the first cavity de Fig. 210.da

of the digestive tube, and that into which the food is immediately re-a ceived, and subjected to the action of the organs of mastication and insalivation. Above and below, it is circumscribed by the jaws, and laterally by the cheeks; anteriorly by the lips and their aperture, constituting the mouth proper; and, posteriorly, it communicates with the next portion of the tube,-the pharynx. It is invested by a mucous exhalant membrane, which is largely supplied with follicles; and into it the ducts from the different salivary glands pour their secretion.

In all animals furnished with distinct digestive organs, means exist for comminuting the food, and enabling the stomach to act with greater facility upon it. These consist, for the most part, as in man, of the jaws, the teeth fixed into the jaws, and muscles by which the jaws are moved.

The jaws chiefly determine the shape and dimensions of the mouth; the upper forming an essential part of the face, and moving only with the head; the lower, on the contrary, possessing great

their course.

mobility. Each of the jaws has a Diagram of the Stomach and Intestines to show prominent edge, forming a semicircle, in which the teeth are implanted. This edge is called the alveolar arch.

1. Stomach. 2. Esophagus. 3. Left, and 4. Right end of stomach. 5, 6. Duodenum. 7. Convolutions of jejunum. 8. Those of ileum. 9. Cæcum.

10. Vermiform appendix. 11. Ascending: 12. Trans

verse; and 13. Descending colon. 14. Commencement of sigmoid flexure. 15. Rectum.

The teeth are small organs, of a density superior to bone; and covered externally by a hard substance called enamel. By many, they have been regarded as bone; but they differ from it in many essential respects, although they resemble it in hardness and chemical composition. At another opportunity we shall inquire into their origin, structure, and developement. We may merely remark, at present, that by many they are looked upon as analogous to the corneous substances, which develope themselves in the tissue of the skin. De Blainville assimilates them to the hair; and believes, that they are primarily developed in the substance of the membrane lining the mouth; and that their enclosure in the substance of the alveolar arches of the jaws occurs subsequently.

VOL. I.-33