opinion as to the seat of hunger is, perhaps, only in our knowledge of the fact that this sensation ceases when food is introduced into the stomach.1 The case is the same in

regard to thirst: the sensation of dryness of the throat is caused by a diminution of secretion in these parts, as well as throughout the organism, in most cases this dryness being accompanied by a diminution of the sweat and urine. The sensations accompanying satiety are also purely general, being sometimes agreeable and sometimes disagreeable, and having, properly speaking, no fixed seat: indeed, hunger and thirst are sometimes experienced in the highest degree, especially in pathological cases, and in cases of non-absorption, in spite of the ingestion of large quantities of food and drink.

The sensations belonging to the other extremity of the digestive tract are more distinct: that, for instance, known as the desire for defecation, the seat of which is not, however, easily defined. It is generally supposed to be situated in the rectum, but it seems more likely to belong to the intestinal tube, as shown by cases of abnormal anus (see p. 278). This sensation indicates simply that the rectum is ready to evacuate the substances with which it is filled. The defecation which follows is an entirely reflex_phenomenon, which we have already studied at length. The agreeable sensation which follows defecation is caused by the overcoming of a difficulty; in place of this, however, in cases of irritation of the intestine or rectum, a peculiar and painful sensation is sometimes experienced, known under the name of tenesmus, producing a desire to throw off the fecal matters even when the intestine is completely empty.

A foreign body produces scarcely any distinct sensation in the mucous of the pulmonary organs: its hardness, its form, and its temperature, are felt very slightly if at all; it, however, produces a vague sensation of pain and uneasiness, and immediately causes a reflex action, giving rise to an involuntary cough, for the purpose of expelling the offending

1 "I have questioned a number of soldiers on this point, choosing carefully those who were ignorant of anatomy, in order that their replies might not be influenced by any involuntary localizing of the sensation. Several among them vaguely indicated the neck or the chest as the seat of hunger, twenty-three indicated the sternum, four could not trace the sensation to any particular spot, while two only designated the stomach. These latter were hospital nurses, and had, consequently, a few ideas in regard to anatomy." Schiff, Physiologie de la Digestion."

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substance. The presence of bodies in these organs is often only discovered after death. The pulmonary surface, properly so-called, appears to be the seat of agreeable sensations (breathing pure air) as well as disagreeable ones (breathing vitiated and confined air); these are, however, in reality, more widely diffused, and, moreover, like hunger and thirst, are connected with the need of the entire organism for a greater or less quantity of oxygen.

The lung may even be said to be much less sensitive than the intestine; we have seen that the latter, in pathological cases, becomes extraordinarily susceptible to impressions; the lung, on the contrary, in a similar case, gives no sign of being diseased, unless the neighboring parts are affected, the pleura, for instance (pleuritis); in general, however, the maladies of the pulmonary surface occasion little pain, and only give rise to a sensation of dyspnea, a vague feeling of discomfort, the seat of which is so little understood that people commonly attribute it to the stomach.

The genito-urinary mucous, that we shall study later, most usually presents only a dull sensation, always subjective, ordinarily unlocalized, and in no wise informing us what cause excites it. Properly speaking, there is no sensation or sensibility in the kidney, testicles, or ovary. We will analyze, farther on, the desire to urinate; we shall find it wholly similar to that for defecation, and shall see also that it is in no less a degree specially localized, and is composed of extrinsic sensations, that we never perceive in those parts where they are actually produced. The sexual desire may, on the one hand, be compared with the desire to urinate, and, on the other, with the desire to breathe, with that of hunger or of thirst, for instance; it is a general desire, produced under the influence of a great number of circumstances, as much internal as external, and that we localize in the sexual organs, because we know the phenomena which take place in them, and that are apt to calm the desire.

The emission of spermatic fluid is accompanied with an agreeable sensation that we refer to the terminal portion of the canal of the urethra, but whose seat is but ill-defined, being situated, like that of the desire to urinate, in the deeper portion (prostatic region), because individuals whose glans has been amputated refer their venereal sensations to the navicular fossa of the urethra which they no longer possess.

The womb has equally a mucous surface of dull, and almost entirely reflex, sensibility, the most important of

whose uses is the expulsion of the fœtus; this is also accompanied with violent pains, characterized always to a greater or less degree by energetic contractions of the smooth muscular fibres. The expulsion is followed by a sentiment of a difficulty overcome, as is that of micturition and defecation, etc. The neck of the womb does not even partake, in spite of numerous nerves, of the sensibility to pain; it can only be the point of departure for certain reflex phenomena: thus it can be cauterized or incised without provoking any sensations; cancer of this organ can become painful only by the development of what we have designated as sympathetic or reflex sensations, and, better still, as associated sensations (p. 57) which radiate towards the sacrum, the thighs, the abdominal walls, etc. (lumbar and sacral plexus).

In order to complete the study of general sensations, we must here say a few words as to the sensibility of the various tissues connected with the surfaces, or placed between them in the deeper portion of the organism. As might be supposed, the muscular, connective, bony, and glandular tissues, have either very little sensibility, or none at all. The muscle may be cut or burned, without producing any very painful sensation, while, if greatly distended, or strongly contracted, it becomes the seat of peculiar vague and painful sensations, such as cramps, which are generally experienced chiefly in the smooth muscles (intestinal, uterine, vesical, colic, etc.). In cases of inflammation this tissue becomes extremely sensitive, as do also the bones, the tendons, the articulating ligaments, and the tissue of the glands themselves. This pathological sensibility is, no doubt, caused by the fact that inflammation, which has a tendency to destroy the organs (especially the muscle), also attacks the nerves contained in them; and because the swelling which nearly always accompanies this pathological process, distends the nerves of the tissue itself, and those of the adjacent tissues, and thus occasions their hyperesthesia: this is the reason that the glands are extremely sensitive to compression, and very painful when swollen.

The muscle appears to possess a peculiar sensibility which forms a sort of transition from general to special sensations; this is what is called the sense of contraction, the muscular sense, by which we know that we have executed movements. What the mechanism and the organs of this sensation may be, is not yet decided (see, farther on, Pacinian corpuscles

of the muscles), but the muscular sense is none the less an indisputable fact. Cl. Bernard has made it certain by various experiments: if all the cutaneous nerves of the limb of an animal be cut, the skin is rendered completely insensitive, although the animal still continues to walk tolerably well, probably because the muscular sensibility is preserved. If the posterior roots (that is, all the sensory nerves, muscular and others) are cut, instead of the cutaneous branches, the movements made by the animal become much less steady. In cases of extensive paralysis in man, when the sensory branches of the muscles are implicated, the patient appears to move his limbs with difficulty, and to be able to do so, only when watching them so as to direct their movements (Cl. Bernard). Finally, some pathological observations have been made in which paralysis of the muscular sense was observed, while the sensibility of the skin remained, or vice versâ (Landry, Axenfeld). This sensibility, or rather muscular sense, enables us to judge of the force and extent of our movements: we judge of their force by distinguishing the difference between different weights, raised one after the other, provided that the variation in the weight of each be at least (Weber); and it is remarkable that the sensibility for lifting weights is much more acute than for the pressure produced by such weight (see farther on, sense of touch); this proves once more that the sensibility of the muscles is entirely distinct from that of the skin.

The study of the muscular sense is still, however, wrapped in such obscurity that some authors (Trousseau) have entirely denied its existence, while others differ greatly in their opinions respecting it: thus Wundt maintains that "the seat of the sensations of motion appears to lie, not in the muscles themselves, but rather in the motor-nerve cells (of the anterior gray matter of the spinal axis), since we experience not only the sensation of a movement performed, but also that of one which has been only intended: the sensation of movement thus appears to be directly connected with motor innervation" (for which reason Wundt designates it as the sensation

1 See Duchenne (de Boulogne), "De l'Electrisation Localisée,” p. 389. Paris, 1872.

Cl. Bernard," Leçons sur la Physiologie et la Pathologie du Syst. Nerveux." Vol. I. p. 246.

Jaccoud, "Les Paraplégies et l'Ataxie du Mouvement." Paris,

of innervation). It is, however, probable that this sensation, by means of which we are made aware of the degree of contraction of our muscles (sense of muscular activity, Gerdy) is the same as that which causes the sensation of fatigue which follows moderate but long-continued exercise, and that its seat lies in the contracted fibres, while the sensation of fatigue experienced after violent exertion appears to reside principally in the tendons (Sappey).

II. SPECIAL SENSATIONS.

THE special sensations render us conscious of external bodies, and of their various properties. They are furnished by the organs of the senses, each of which supposes, 1, an organ susceptible to the impression; 2, a nerve, by means of which the impression is transmitted; and 3, a central part of the brain by which the impression is received and understood.

The peripheral organ, which first receives the impression, proceeds always from a more or less modified part of the cutaneous and external surface (epidermis), or of the most primitive parts of the internal surface (epithelium): thus we have, as organs of the senses proceeding from the skin, the

1 See also researches by Bernhardt (Zur Lehre von Muskelsinn. Analysé, en "Revue des Sciences Médicales," de G. Hayem. Vol. I. p. 61, 1873). This author holds, with J. Müller, Ludwig, and Bernstein, that the muscular sense simply consists in the faculty of exactly estimating the intensity of the excitation which, beginning in the encephalon, results in the movement intended. He found, after causing the contraction of the muscles by faradization (the interrupted current) that the person experimented upon experienced much greater difficulty in recognizing the variation between different weights than when the contraction was produced by the influence of the will. From this Bernhardt concluded that the sense of force is a psychical function. He admits, however, that the sensory impressions beginning in the soft parts adjacent to the muscles have a powerful influence in completing the notion or idea formed by the centres of volition. According to him, therefore, the muscular sense, properly so called, has no existence. Trousseau, considering the subject from a similar point of view, has also denied the existence of the muscular sense, referring every thing to the sensibility of the soft parts displaced by the movement. Ataxie, en " Nouv. Dict. de Méd. et de Chir. Prat." p. 776.)

See Art.
Vol. III.