stature. Dr. Hutchinson also found that the capacity of the lungs bears a uniform relation to the height of the individual, increasing eight cubic inches for every inch above five feet; and, lastly, he discovered that when we are sitting or lying down there is a considerable diminution in the capacity of the lungs for containing air; being in the former case lessened from 260 to 255, and in the latter to 230 cubic inches. After a hearty meal, too, the capacity of these organs is lessened from ten to twenty cubic inches.*

And now, before I close this Lecture, let me say a few words in reference to the trachea or windpipe, and the bronchial tubes. You see that the former is nearly a cylindrical tube, and forms the common air passage to both the lungs. It is partly situated in the neck and partly in the chest, and measures from about four to four and a half inches in length. Its structure consists of from sixteen to twenty cartilaginous rings, connected with each other by a ligamentous substance mixed with muscular fibres. It is to be noticed that these cartilaginous rings are, however, not quite complete, for they terminate behind in a muscular and ligamentous membrane, which, whilst completing the tube, admits yet of compression. Loose cellular tissue surrounds the trachea, so that it can move freely on the surrounding parts. You observe this other tube behind it. This is called the esophagus or gullet. It is the canal down which all that we eat and drink passes. It is covered with a soft membrane, secreting a mucous fluid, which defends the surface from the acrimony of the air.

Now let us see the course which the trachea takes. You notice that after it has passed down the neck it divides as it enters the chest into two parts, one for each lung; but you perceive they differ from each other in size and direction. These two smaller tubes are called the bronchi (from the Greek word Boyxos, the throat), and you will remark that they differ from each other in size, and also in the course they take. The right bronchus is shorter but wider than the left, and is usually about an inch in length, while the left bronchus is nearly twice as long. Their general structure resembles that of the trachea. The number of rings in the right bronchus varies from six to eight; in the left from nine to twelve. Before penetrating the substance of the lungs, the bronchus divides again into further branches, one being intended for each lobe of the lungs. As they proceed, they still further ramify through the lungs, becoming smaller and smaller, and the cartilaginous rings less and less distinct, until finally they quite disappear, so that the air-cells in which they terminate appear to be but an extension of the mucous membrane which lines the bronchi. It is evident that the cartilaginous structure of the trachea and bronchi serves to keep the air-passages open; and it has been suggested that if we do not find them in the minuter branches, the probable cause is that they can never be completely emptied of air after the first inspiration of "the breath of life" has been taken at the time of birth.

Now, as the proper regulation of the act of respiration is one of the most important things to be attended to by the public speaker or reader as * Medico. Chi. Transactions, vol. xxix.

regards health and comfort in himself, as well as the effectiveness of his delivery upon his audience, I think it right to enter somewhat fully into a description of the mechanism of respiration.

Two distinct processes, dependent upon each other, constitute the act of respiration. The one is called inspiration and the other expiration. Let us examine these, in their order, a little in detail. We have seen already that that movable frame, the thorax, is, by the action of its muscles, capable of being enlarged transversely by the elevation of the ribs, and vertically by the descent of the diaphragm. When we take a full inspiration, the levatores costarum and the intercostal (and, in women especially, what are termed the scaleni muscles) elevate the ribs. At the same time the diaphragm descends as the ribs rise, which causes the abdominal viscera to be pushed down. Thus the thoracic cavity is enlarged in all directions; the lungs expand in proportion, and a vacuum of some extent is formed within their air-cells. A mechanical consequence follows. The denser external air, possessing greater gravity than the air within the chest, rushes through the nostrils into the trachea to occupy the vacuum that has been formed, and with this ends the act of inspiration. After this the intercostal and other muscles begin to relax, and gradually the ribs are restored to their former position, partly by their own elasticity and partly by the external pressure of the surrounding atmosphere. At the same time the abdominal muscles react, and the diaphragm rises up, and resumes its former position as the floor of the chest. The inflated lungs contract, too, simultaneously; the air that has by the former process been taken in is now forced gradually out, and the thoracic cavity is restored to its former dimensions, and so concludes the act of expiration. Common experience will tell us how greatly the acts of inspiration and expiration vary in degree. When, for instance, we are sitting quietly studying or writing, respiration is performed almost entirely by the rise and fall of the diaphragm, and we can scarcely perceive the movement of the ribs. But now let us rise from our books or papers, and refresh ourselves with a good, deep inspiration, and we shall at once find how much more vigorously ribs, diaphragm, and all the muscles of respiration are acting. Let us, as an experiment, try to inspire as much air as we possibly can, and we shall feel that the diaphragm has now descended to its lowest degrees, while the chest has, by the action of the various muscles I have before spoken of, become enlarged to its utmost capacity. It is just the same as regards the reverse process when we increase the force and depth of our acts of expiration. Occasional exercises of the organs of respiration in this way are very serviceable for giving them vigour and flexibility of action, besides contributing to the general health of the system for there can be no question that the grand object of respiration is, as we have already seen, the regular purification of the blood, which, as it courses through the body, becomes charged with noxious elements, that, if retained, would be absolutely destructive to life; but, by the blood being constantly brought into contact with the air, the poisonous constituents of venous blood are eliminated, and from the new elements, derived from the atmosphere, it is converted into the pure, bright arterial blood. This is the primary result of respiration;

but there is another secondary effect, scarcely less essential to life and physical well-being; and that is the evolution of heat, or caloric, as it is scientifically termed; and this is produced chiefly, if not entirely, by the chemical combination of the carbon of the blood with the oxygen of the atmosphere. All this will show you how important it is in every way that the lungs should be regularly and properly exercised. I have now, then, finished all I have to say in regard to the organs and functions of respiration, and in my next Lecture I hope more especially to bring before you the subject of the vocal and speech organs, and to show you how voice is produced, and afterwards converted into man's grand prerogative articulate language.

LECTURE IV.

General Description of all the Vocal Organs and their Respective Functions, with Illustrative Drawings-The Discoveries made by means of the Laryngoscope and its History -Formation of Voice by the Vocal Cords-Results of the Experiments of Garcia, Türck, Czermak, Sir G. D. Gibb, and others-Drawings of the Vocal Cords when at rest in silent Respiration and when producing Voice-Change of Voice at PubertyRetention of the Effeminate Voice in Manhood, and proper Mode of Cure-Auxiliary Organs of Voice-Voices of Animals-Quotation from Dr. Carpenter-Brief Summary of the Articulating Organs.

N my last Lecture I described to you fully the chest and those respiratory organs which are subservient to the phenomena of the voice. This evening I propose occupying your attention with an examination of the structure and functions of those organs which are more immediately concerned in the

production of voice.

Let me, as I did on the former occasion, endeavour to render my remarks the clearer by a reference to the drawings and diagrams before you, and the first to which I call your attention is this, which is the external appearance presented by the larynx. (See Fig. 3.)

And next I have to bring before your notice this, which represents a section and exhibits the interior of the larynx. (See Fig. 4.)

And then this, which exhibits the interior of the air-passage in a larynx and trachea slit down behind. The letters in the preceding drawing refer also to this. (See Fig. 5.)

It is a most delicate, complicated, and important organ, for it is the instrument that produces all vocal sound. You see it is situated in the anterior portion of the neck, and rises out of the windpipe, and it consists of five principal elastic cartilages, of which one is always very perceptible to the eye, and two of them still more discernible through the integuments that cover them by the sense of touch. Let us then examine them in detail. The tube thus composed is itself called the larynx. This cartilage, G, which you see here connected by ligaments and membranes to the first ring of the windpipe, is called the cricoid, or ring-shaped cartilage. It is, as you can feel by placing the finger on your own necks just at that spot, very firm and solid in structure, serving, in fact, as a substantial foundation for the parts above it. Above this you notice a very marked cartilage. This is termed the thyroid, or shield

shaped, cartilage. It is composed of two portions, which unite in front, forming a decided protuberance in the throat of the full-grown man. It has received the fanciful appellation of the pomum Adami, or Adam's apple, from the strange idea, or legend, that a portion of the forbidden fruit stuck in his throat, and has in appearance been perpetuated in all his descendants. The thyroid differs from the cricoid cartilage in this, that it does not surround the larynx, but at the back presents at its

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Fig. 3.

External aspect of the larynx, trachea, and thyroid gland. 1. Thyroid cartilage. 2. Cricoid cartilage. 3 3. The superior horns of the thyroid cartilage. 4 4. The thyroid gland. 5. The trachea. 6. Bifurcation of the trachea. 7. Subdivision of the bronchi.

extremities prolongations upwards and downwards, E and F. The former are called its great horns, and are connected by ligaments to the tongue-bone, while the latter are much shorter, and are connected by muscles and ligaments to the cricoid cartilage.

Now, then, I come to two cartilages much smaller than the others, H. They are named the arytenoid or ewer-shaped cartilages, and are placed in the highest part of the cricoid cartilage. In shape they are pyramidal, and are so connected to each other and the other cartilages by muscles