and cursory glance at those intellectual faculties which have been bestowed on man for the government and direction of the powers of which I have been speaking.

Hence I shall have to notice the mysterious functions of the BRAIN and NERVES, which constitute the parts of our bodies which are in the nearest relation to the intellectual faculties; and to touch on that highly-interesting and important subject, the cultivation and right use of the MIND.

Notwithstanding the strictest attention to the best principles and rules which can be laid down for the preservation of life and health, man, like the lamp to which I have been comparing him, sooner or later yields to the all-conquering hand of time;-the admirable and complicated machine is dissolved, and its place is supplied by a new machine.

The process by which the perpetuation of the species is insured, notwithstanding the dissolution of the individuals who compose it, has no counterpart amongst the works of man's contrivance.

Here, then, I abandon my simile; after remarking, that as, before the flame ceases to flicker in the exhausted socket, the vital spark may be communicated to another lamp, and burn with renovated vigour; so the passing generation will live in that which succeeds it, and the energies of an emulous posterity may be conspicuous, either as a shining light, or as a burning shame.

My Fourth Lecture will be devoted to this subject; in reference to which, the duties of the PRESENT and the claims of the SUCCEEDING GENERATION will be pressed on your serious attention.

The limits to which I must confine myself in the

Four Lectures, of which I have given the outlines, will necessarily prevent me from entering into minute details. I shall endeavour briefly to explain principles, and offer a few suggestions; which must be regarded rather as specimens of the application, than the notice of all that should be done.

AIR, LIGHT, CLEANLINESS, CLOTHING.

A function or process, in its nature resembling what we call respiration or breathing, is performed by all living beings. Even plants breathe; and their leaves are the organs by which their respiration is performed. Polypi, of which you have an example in the jelly-fish, and zoophites, of which you may take sponge for an example, which constitute the lowest links in the chain of animals, perform this function by the whole of their exposed surfaces; but in all animals higher than these, there is a special apparatus for this purpose. In those which live in the water we find various modifications of gills. Thus in the lobster and crab, which belong to a class of animals called crustacea, you know there are spongy bodies, called by some persons dead-men's flesh. The oyster, which belongs to another class of animals called mollusca, breathes by means of that part which resembles a fringe, and is called the beard; whilst in the true fish, such as the herring and the shark, we find for the same purpose those parts which are generally known by the name of gills; but even in these there is some variety. On the other hand, those animals which either live in air, or at least breathe it, are provided with lungs, or with organs bearing some resemblance to them. The snail, which I mention as animals, or mollusca living in

a specimen of the soft

air, has a kind of lung. The caterpillar, and the animals allied to it, of the insect class, are furnished with two tubes, one on each side of the body, for the reception of air, which finds its way into and out of them by two corresponding rows of small pipes or pores called stigmata. Frogs, turtles, serpents, and other reptiles, have regular lungs, but of a coarse texture : birds breathe by means of lungs of a fine texture, which have, as accessories, various large cavities which receive air from the lungs.

Man, as you know, and those animals which belong to the same class with him, breathe by means of very perfect lungs, which occupy a considerable part of the trunk. The air enters them by the windpipe: this divides; and its branches again and again divide and sub-divide, till its small and delicate branches have conveyed the air into the soft and spongy structure of the lung, in which it is brought into intimate contact with the organ. In man, and in those animals which resemble him in their mode of breathing, the process of respiration is partly mechanical, and partly chemical.

The mechanical part consists in the admission of air, by the expansion of the cavity; which is brought about by the raising of the ribs, and the descent of the diaphragm or midriff; and in the expulsion of the air, when the capacity of the chest is diminished by the falling of the ribs and the raising of the diaphragm. In its passage between the mouth and lungs, the air may be stopped at a narrow part, a little behind the tongue, called the rima glottidis. This may happen at our own will, or, at times, by serious or even fatal accident. The air, as it is put in motion in the lungs by the act of taking in and

sending out breath, produces a sound which may be heard through the ribs, and which differs in the healthy and the diseased states of the lung. On this fact is founded the use of the cylinder or stethoscope, an instrument of great advantage in the investigation of the diseases of the chest.

The chemical part of the process consists chiefly in the loss of oxygen gas, and the formation of carbonic acid gas: the one is generally equal to the other. There is, however, some difference, in this respect, between summer and winter. Sometimes there is not merely a loss of a part of the oxygen in the respired air the quantity of the azote, the other component part of the atmosphere, may likewise be altered: this seems to depend on the season of the year, and on the state of the animal, and particularly on the situation in which it had been placed previously to the examination. The number of respirations per minute varies in different persons, and also in the same person at different times: the mean may be stated at twenty. About one-eighth of the air in the chest is changed in each ordinary act of respiration and inspiration; and, on an average, 666 cubic feet of air are breathed in twenty-four hours.

*

The general conviction of the close connexion between breathing and life is shewn by the expressions, “breath of life,” “breathing one's last," "expiring," and the like. The absolute necessity for the constant performance of the changes effected by respiration is fully demonstrated by experiments on animals

* For further details respecting the quantity of air inhaled and vitiated by respiration, consult Dr. Edwards on the Influence of Physical Agents on Life; translated by Dr. Hodgkin and Dr. Fisher, Sir H. Davy, Dr. Bostock, and Dr. Menzies.

which perform the function in water, as well as on those which breathe air. Thus fish die in limited quantities of water, if contact with air be prevented; and the effect will be more striking if the air contained in water has been expelled by boiling.

We need not, then, be surprised at the serious and not unfrequently fatal consequences of those circumstances which interfere with respiration. I shall notice these under different heads.

I.

1. Man, or any other animal, may die from having only a limited quantity of air, which he contaminates himself, and renders unfit for the purposes of life; as when a small animal is placed under a receiver, or when human beings have been confined in airtight chambers, cases of which kind have occurred in mines, on the irruption of water. As our rooms are not air-tight, it is rare for immediately fatal effects to proceed from the contamination of the air in them by means of the continued respiration of the same portion; yet instances have occurred of persons perishing from close crowding in a confined apartment, of which few instances are more fatal or striking than the case of our countrymen confined in the BlackHole at Calcutta. This was in 1756; when the Indian Nabob, Surajah Dowla, consigned 146 prisoners to the dungeon so named.

"It was about eight o'clock when these unhappy persons, exhausted by continued action and fatigue, were crammed together into a dungeon about eighteen feet square, in a close sultry night, in Bengal; shut up to the east and south, the only quarters whence