M, the mouth is shut by the lips; for N, by the application of the tongue to the palate.

28. The other consonantal sounds of the English language are produced by shutting the passage through both nose and mouth; and, as it were, forcing the expiratory vocal current through the obstacle furnished by the latter, the character of which obstacle gives each consonant its peculiarity. Thus, in producing the consonants B and P, the mouth is shut by the lips, which are then forced open in this explosive manner. In T and D, the mouth passage is suddenly barred by the application of the point of the tongue to the teeth, or to the front part of the palate; while in K and G (hard, as in go) the middle and back of the tongue are similarly forced against the back part of the palate.

29. An artificial larynx may be constructed by properly adjusting elastic bands, which take the place of the vocal chords; and, when a current of air is forced through these, due regulation of the tension of the bands will give rise to all the notes of the human voice. As each vowel and consonantal sound is produced by the modification of the length and form of the cavities, which lie over the natural larynx, so, by placing over the artificial larynx chambers to which any requisite shape can be given, the various letters may be sounded. It is by attending to these facts and principles that various speaking machines have been constructed.

30. Although the tongue is credited with the responsibility of speech, as the "unruly member," and undoubtedly takes a very important share in its production, it is not absolutely indispensable. Hence, the apparently fabulous stories of people who have been enabled to speak, after their tongues had been cut out by the cruelty of a tyrant, or persecutor, may be quite true.

Some years ago I had the opportunity of examining a person, whom I will call Mr. R., whose tongue had been removed as completely as a skilful surgeon could perform the operation. When the mouth was widely opened, the truncated face of the stump of the tongue, apparently covered with new mucous membrane, was to be seen, occupying a position as far back as the level of the anterior pillars, of the fauces. The dorsum of the tongue

could discern None of these

was visible with diffculty; but I believe I some of the circumvallate papillæ upon it. were visible upon the amputated part of the tongue, which had been preserved in spirit; and which, so far as I could judge, was about 2 inches long.

When his mouth was open, Mr. R. could advance his tongue no further than the position in which I saw it; but he informed me that, when his mouth was shut, the stump of the tongue could be brought much more forward.

Mr. R.'s conversation was perfectly intelligible; and such words as think, the, cow, kill, were well and clearly pronounced. But tin became fin; tack, fack or pack; toll, pool; dog, thog; dine, vine; dew, thew; cat, catf; mad, madf; goose, gooth; big, pig, bich, pich, with a guttural ch.

In fact, only the pronunciation of those letters the formation of which requires the use of the tongue was affected; and, of these, only the two which involve the employment of its tip were absolutely beyond Mr. R.'s power. He converted all t's, and d's into f's, p's, v's, or th's. Th was fairly given in all cases; s and sh, i and r, with more or less of a lisp. Initial g's and k's were good; but final g's were all more or less guttural. In the former case, the imperfect stoppage of the current of air by the root of the tongue was of no moment, as the sound ran on into that of the following vowel; while, when the letter was terminal, the defect at once became apparent.

LESSON VIII.

SENSATIONS AND SENSORY ORGANS.

1. THE agent by which all the motor organs (except the cilia) described in the preceding Lesson are set at work, is muscular fibre. But, in the living body, muscular fibre is, as a rule, made to contract by a change (Lesson V. §31) which takes place in the motor or efferent nerve, which is distributed to it. This change again is generally effected by the activity of the central nervous organ, with which the motor nerve is connected. The central organ

is thrown into activity, directly or indirectly, by the influence of changes which take place in nerves, called sensory or afferent, which are connected, on the one hand, with the central organ, and, on the other hand, with some other part of the body. Finally, the alteration of the afferent nerve is itself produced by changes in the condition of the part of the body with which it is connected; which changes usually result from external impressions.

2. Sometimes the central organ enters into a state of activity without our being able to trace that activity to any direct influence of changes in afferent nerves; the activity seems to take origin in the central organ, and the movements to which it gives rise are called spontaneous,' or 'voluntary.' Putting these cases on one side, it may be stated that a movement of the body, or of a part of it, is to be regarded as the effect of an influence

(technically termed a stimulus or irritation) applied directly, or indirectly, to the ends of afferent nerves, and giving rise to a modification of the condition of the particles or molecules which form the substance of the nerve fibres, i.e. to a molecular change, which is propagated from molecule to molecule along the fibres to the central nervous organ with which these are connected. The molecular activity of the afferent nerve sets up changes of a like order in the fibres and cells of the central organ; from these the disturbance is transmitted along the motor nerves, which pass from the central organ to certain muscles. And, when the disturbance in the molecular condition of the efferent nerves reaches the endings of those nerves in muscular fibres, a similar disturbance is communicated to the substance of the muscular fibres, whereby, in addition to the production of certain other phenomena to some of which reference has already been made (Lesson V. § 31), the particles of the muscular substance are made to take up a new position, so that each fibre shortens and becomes thicker.

3. Such a series of molecular changes as that just described is called a reflex action: the disturbance in the afferent nerves caused by the irritation being as it were reflected back, along the efferent nerves, to the muscles. But the name is not a good one, since it seems to imply that the molecular changes in the afferent nerve, the central organ, and the efferent nerve are all alike, and differ only in direction; whereas there is reason to think that they differ in many ways.

A reflex action may take place without our knowing anything about it, and hundreds of such actions are continually going on in our bodies without our being aware of them. But it very frequently happens that we learn that something is going on, when a stimulus affects our afferent nerves, by having what we call a feeling or sensation. We class sensations along with emotions, and volitions, and thoughts, under the common head of states of consciousness. But what consciousness is, we know not; and how it is that anything so remarkable as a state of consciousness comes about as the result of irritating nervous tissue, is just as unaccountable as any other ultimate fact of nature.

4. Sensations are of very various degrees of definiteness. Some arise within ourselves, we know not how or where, and remain vague and undefinable. Such are the sensations of uncomfortableness, of faintness, of fatigue, or of restlessness. We cannot assign any particular place to these sensations, which are very probably the result of affections of the afferent nerves in general brought about by the state of the blood, or that of the tissues in which they are distributed. And however real these sensations may be, and however largely they enter into the sum of our pleasures and pains, they tell us absolutely nothing of the external world. They are not only diffuse, but they are also subjective sensations.

5. What is termed the muscular sense is less vaguely localised than the preceding, though its place is still incapable of being very accurately defined. This muscular sensation is the feeling of resistance which arises when any kind of obstacle is opposed to the movement of the body, or of any part of it; and it is something quite different from the feeling of contact or even of pressure.

Lay one hand flat on its back upon a table, and rest a disc of cardboard a couple of inches in diameter upon the ends of the outstretched fingers; the only result will be a sensation of contact-the pressure of so light a body being inappreciable. But put a two-pound weight upon the cardboard, and the sensation of contact will pass into what appears to be a very different feeling, viz., that of pressure. Up to this moment the fingers and arm have rested upon the table; but now let the hand be raised from the table, and another new feeling will make its appearance-that of resistance to effort. This feeling comes into existence with the exertion of the muscles which raise the arm; and it is the consciousness of that exertion which goes by the name of 'the muscular sense.'

Any one who raises or carries a weight knows well enough that he has this sensation; but he may be greatly puzzled to say where he has it. Nevertheless, the sense itself is very delicate, and enables us to form tolerably accurate judgments of the relative intensity of resistances. Persons who deal in articles sold by weight are constantly enabled to form very precise estimates of the weight of such articles by balancing them in their hands; and in