parotid gland of the sheep. It is in the lobules, which are of course lined with mucous membrane, that the secretion takes place; it is then conveyed into the little tubes, which terminate in a common duct, opening on a free surface.

The composition and use of the saliva has lately excited a good deal of attention; but it is obvious that however much it may assist in the digestion of solid food, very little of it is taken into the stomach with food that is swallowed without mastication. When saliva is chemically examined, it is found to consist of water, various salts, and a quantity of organic matter called ptyalin, or salivin. The universal presence of this latter substance has led to the conclusion that it plays an important part in the process of digestion. Ptyalin belongs to a class of substances which speedily decompose, and even communicate this property to other bodies with which they may come in contact. These bodies act, in fact, on substances in the same way as yeast acts when it is placed in contact with saccharine solutions. They produce chemical changes which go under the name of fermentation. It appears, then, not improbable—although it has not been demonstrated that the ptyalin of the saliva entering the food, predisposes it to pass into those changes, which ultimately facilitate the process of digestion. The salivary glands are sometimes inordinately excited, and secrete large quantities of saliva. This condition, when permanent, is called salivation. Some medicines have the power of producing this state of the glands. Some act by directly stimulating these glands, as tobacco, mezereon, &c.; whilst others, as mercury, act on them through the constitution. Except produced as remedies for more serious disease, excessive salivation should be avoided. Hence the practice of spitting when tobacco is either chewed or smoked, is frequently productive of ill consequences; and attacks of indigestion, and nervous derangement, have been traced to the practice. The flow of the saliva is also, to a certain extent, affected by the mind. The "watering of the mouth," at the sight of things known to be pleasant to the palate, is a fact familiar to the experience of all.

We may now proceed to trace the food in its exit from the mouth. No sooner is

the food passed from the tongue into the pharynx (Fig. 8, c), than it is removed from the influence of the will. The muscles that move the jaw-those which line the inside of the cheek (Fig. 8, a),—and those of the tongue, are, to a great extent, under the direction and control of the will; but the pharynx, and gullet, or oesophagus (Fig. 8, c and f), are supplied with muscles which are quite independent of the will, and over the actions of which we have no control. Henceforth we commit the important processes through which our food has to pass before it can be part and parcel of the body, to forces and functions of which we are entirely unconscious.

During the passage of the food into the gullet (Fig. 8, f), two things have to be guarded against. The first is the entrance of the food into the nostril at the back through what is called the posterior opening of the nares, which communicates with the pharynx. The second is the passage of the food into the larynx or windpipe, (Fig. 8, d). The first object is obtained by the formation of the soft palate, which consists of a fold or veil of mucous membrane, containing muscular fibres, the lower edge of which hangs free, and has depending from the middle the uvula, which may be seen on looking into the back of the mouth while the breath is taken. On the food passing into the pharynx, this veil of membrane is carried back, and prevents the food from getting upwards into the nose. Should, however, a fit of laughing, or any other cause of a strong expiration of air from the lungs, occur at the moment of swallowing, the soft palate is thrown forward, and the disagreeable effect is experienced of the food passing into the nostrils.

The liability of the food to pass into the larynx is a more dangerous one, not less carefully provided against. At the upper part of the larynx (Fig. 8, d), is a chink called the glottis. The air in breathing passes in and out of this space, in order to pass to the mouth and posterior nares. The membranes constituting the glottis are supplied with nerves which render it exceedingly sensitive to external impressions. A small particle of food or drink falling on it, will excite violent coughing, and sometimes spasmodic closure of the orifice. Yet over this delicate chink, all the food taken into

the human system must pass before it arrives at the stomach. Its protection, however, is provided for by the existence of a small valve-like body, called the epiglottis, which, during the act of swallowing, passes down over the glottis, and effectually closes it against the passing into it of any stray portions of food.

The same causes, however, which sometimes interfere with the action of the soft palate, will also serve to prevent the falling down of the epiglottis; and the consequences, to which we have before alluded, will take place.

The structure of the gullet, or esophagus (Fig. 8, f), need not detain us long. It is surrounded by muscular fibres, which assist in propelling the food, and is lined internally with a mucous membrane, which is a continuation of that in the mouth. The gullet opens into the stomach, and both its muscular and mucous structure are continued into this organ: the more particular description of which we must reserve for our next chapter.

THE ART OF THINKING. FROM THE FRENCH OF DEGERANDO.

(Continued from Page 89.) IN the hope of rendering the application of rules easy and certain, they have become purely mechanical, and consequently deprived of their true principle of action, both morally and intellectually. Rules have been laid down as to how to select a subject, how to determine it, how to circumscribe and divide it; the proper times and places for action and repose, for ideas and emotions, have been assigned; the boundaries, the method and formularies, have all been laid down; the exercise of the moral and intellectual faculties has been rigorously bound by a preconceived system, utterly neglectful of the fact, that in order that the faculties should fulfil their destined functions, a certain degree of independence is necessary, and that the first and most indispensable requisite for thinking is, the acquirement of that energy and freedom of the mind, which allows the soul to appropriate to itself the truths on which it meditates, as if they sprung spontaneously from the depths of its own being.

The truth is, that in reference to the Art of Thinking, the difficulty does not lie so much in the act itself, as in the commencement of the act; not so much in the cultivation of the soil, as in the taking possession of it. The shores of the regions of thought are steep and rugged, and inspire feelings of affright and terror to those who first approach them. This is the true reason why the Art of Thinking is really practised by so few. In first attempting this difficult process, we are repulsed on all sides; memory assails us with a thousand reminiscences in the retreat we may have chosen; capricious and wandering phantoms of objects, long since removed from us, return and importune us more than the objects themselves ever did, crowding round us in every direction. If we strive to appease this tumult, a still more painful state often awaits us-blank void, and obscurity. Instead of those fertile regions where we had hoped to wander in joyous happiness, we discover a parched desert; it is in vain that we attempt to call up those heavenly images that were to transport us to Elysium; they fly from us, and we fall back upon ourselves, overwhelmed with weariness, the mind seeming but a vast solitude. By another effort the clouds become dissipated; ideas present themselves, yet confused, incoherent, and disordered; they escape us the moment we try to seize them; they confusedly mix and interfere with each other, and end by plunging us in a state the most painful of all, viz. doubt and scepticism. It is only when we have the courage to traverse these three successive zones, so to speak, that we come at last to that luminous and peaceful sphere, where the fruit of meditation and all its pleasures await us; but we are too often discouraged, and renounce the enterprise as impossible.

A most important thing therefore is, to facilitate the entrance to these regions of thought: and this can be effected only by a suitable preparation, the proximate result of which is the attainment of that state of mind which we usually term self-possession. Self-possession, however, does not exclusively consist, as some mystical writers have imagined, in isolating the soul from every external influence. It is the gathering together of all the powers of the mind, and the disposing of them with sovereign

questions itself, and should wait the reply, and receive it with confidence and with entire good faith; there should be no suggestion of the reply, for we learn only what we have a sincere desire to learn. All men have very nearly the same primitive or fundamental notions, particularly as regards moral subjects; the chief difference is, that some know how to cultivate and develop them, while others neglect and disuse them. That restless agitation of the mind which arises from our very anxiety to develop its powers, affects chiefly those inexperienced in the art of thinking. There is nothing more difficult of comprehension than a mental state of calm activity, because there is nothing more difficult than complete selfpossession in the midst of action; we pass from sleep to agitation, and fall again from agitation into sleep; the impatience of success makes us blind to the true means of attaining it.

There is no successful thinking without method, which is rendered doubly needful in moral meditations, since the mind cannot here rest on any extraneous aids, and is therefore in constant danger of falling into vague incoherency. This method, however, need not have all the vigour and precision of science, for this would entail upon it something of the dryness of science; it should be natural and simple, in order to allow entire liberty to the mental movements, and to the springs of emotion in the heart; it consists at first in dissipating the clouds in which ideas are usually involved, in clearly distinguishing them, in distributing and arranging them, and in clearly discerning the end of thinking itself. If this be perfectly apprehended, precise views will spring up in abundance, as in Geometry, when the position of the problem is once established, the means of solution readily and naturally present themselves. Method will lead to the discovery of those parent thoughts, which contain the germs of numberless others, and at the same time enable us to seize their connecting links; it will fix the rank and relation of each separate consideration-reduce to unity the scattered notions which float on the surface of the mind-assign to them a determinate place -make them reflect light on each other, and develop from them their practical applications. The mind has a tendency to fall into vague and idle reverie where the

natural labour of thought is replaced by a soft mental voluptuousness, in which we cannot properly be said to think at all; we become, on the contrary, oblivious and dreaming, or rapt in a state of vain or false ecstacy. This is a dangerous state, and clearly arises from such a want of method as allows this state of confusion and anarchy.

The advantages of thinking do not follow immediately, nor after a first trial; the success obtained will vary according as we mix up with these secret operations of nature those varying states of the mind which often arise quite independently of the will. Perseverance is essential to success: both clearness and freedom will be gained by it, for it is especially necessary that on many points we should dwell long and patiently, in order that we may completely develop all that the subject may involve. Barrenness of intellect is generally a consequence of precipitation. In moral meditations, the tranquillity which attends steady perseverance is necessary, in order that from the conceptions of the reason may flow the emotions which should fill the heart. The spring of those emotions demands a certain amount of quiet contemplation; just as in the admiration excited by the highest works of art, time is required to develop all their beauty. The soul must have leisure to perceive the emanations of the true and the good; to feel them, appropriate them, and transform them, as it were, into its own proper substance. There is even danger in considering too many objects; each should be thoroughly digested, and, in developing itself, display all the fertility that belongs to it.

Finally, in order that meditation should produce its greatest effect, it should be appropriately recapitulated, and presented in simple formulæ, that it may without difficulty be fixed in the memory, and be made easily applicable to the wants and duties of daily life. Method in these exercises will render this last operation easy, particularly if we once acquire the habit of carrying into practice the truths which flow from meditation. Contemplation and action too often assume a sort of rivalship to each other, and dispute possession of man; the former has its most zealous advocates with mystical writers; the other