and by a very simple mechanism, they convey their contents into the bladder without a possibility of regurgitation, merely by passing obliquely about half an inch between the muscular and inner coats of that organ, which oblique entrance answers every purpose of a valve.

OF THE INTEGUMENTS OF THE BODY. The human body is protected by a strong pliable and sensible covering, which not only defends the parts beneath from external injury, but gives symmetry and beauty to the figure. This covering consists of several parts, which we shall enumerate, and briefly describe.

Of the cellular Membrane and Fat. Between the skin and the muscles, or flesh, and between the fibres of each muscle, there is interposed a loose, oily substance, composed of a cellular texture and fat. The latter is fluid in the body, and is deposited in the cells of the former, for facilitating muscular motion. The cellular membrane, which contains this fat, is not confined to any particular part, but exists at every point of the body. It serves as a bond of union, by tying and fastening all the parts together, yet in such a manner as not to prevent or obstruct their necessary motions. Fat is deposited very unequally throughout the body, but it is always found where it seems to be most wanted. It fills up the chinks and crevices of the muscles, and it gives that gently undulating outline to our bodies, on which the beauty of the human form depends. It undoubtedly answers many other purposes. It is supposed to accumulate in health and middle age for the supply of the system when other sources fail. Hence it is absorbed in disease, and taken up into the circulation. In old age its quantity lessens when the appetite and other functions fail.

Of the Skin. The skin of the human body consists of three separate parts or layers, which lie in close contact with each other, and adhere by means of numerous small vessels, and fibres which pass from one to the other. The first layer,

called the cutis, or true skin, is spread immediately upon the fatty membrane just described, and is always white, whatever the complexion may be. This skin is very vascular, and is endowed with exquisite sensibility, being supplied with numerous nerves, whose papillæ stand out, and are the seat of feeling. It is extremely elastic, as in the dropsy it will stretch out very far, and return again with health, nearly to its natural dimensions. Under the inferior surface of this skin, there are situated numerous small glands, which secrete an oily fluid, poured out upon the external surface of the skin by means of excretory tubes, to keep it soft and flexible. It is this skin in animals, which, when prepared by tanning, constitutes what is called leather.

Immediately on the surface of the true skin, between it and the cuticle, or scarf-skin, is-interposed a mucous substance, on which depends the colour of the body. Externally to this mucous membrane lies the cuticle, or scarf-skin, which is a fine, transparent, but insensible membrane, every where investing the body, and is the part of the skin which is raised in the form of bladders, by the operation of fire or a blister. The use of this last covering of the body is to protect the delicate nervous fibres, which stand out from the true skin, from the external air, and to modify their too great sensibility, by interposing itself between them and the body in contact. The cuticle is perforated by innumerable pores, for the passage of the perspirable matter.

Of Perspiration. An important office of the skin, is to exhale from the body a part of the watery fluid which it contains, and for this purpose it has innumerable excretory vessels opening upon its surface. This exhalation, though frequently insensible, is perpetually going on, as will be evident, by plunging the naked arm into a long, but perfectly clean and dry glass receiver. The vessel will soon lose its transparency; and if the arm be kept in it some time, streaks of moisture will trickle down the sides of the glass. Hence it is evident, that the matter of perspiration has water for its basis, and that

this water is perpetually flying off in subtle vapour, or when the action of the perspirable vessels is increased either by exercise or heat, the perspiration becomes more sensible, and is seen to exude from the skin in large quantities. One of the great uses of perspiration is to regulate the system, by keeping up a constant evaporation.

Of the Hair and Nails. Hairs consist of an insensible excrescence produced from the cutis. Each hair grows from a small bulb, and is lengthened by means of additions made to it in the bulb. The bulbs, when viewed with a microscope, are found of various shapes. In the head they are roundish, and in the eye-brows oval. Each bulb seems to consist of two membranes, between these there is a certain quantity of moisture. Within the bulb, the hair is separated into three or four smaller fibres. The bodies of the hairs, that is, the parts without the skin, vary in softness and colour according to the difference of climate, age, temperament of the body, &c. They afford a light and ornamental covering to the head, and, as in the case of the eye-lids and brows, serve as a defence to the delicate organs of vision: and they frequently adorn the figure by the richness of their colour, and the beautiful tresses which they form.

The nails are hard, and partly transparent, like horu. They seem to possess many properties in common with the scarf-skin; like that substance they are neither vascular nor sensible, and when the scarf-skin is separated from the true skin by maceration, or otherwise, the nails frequently come away with it. In each nail we distinguish three parts, the root, the body, and the extremity. The root is a soft, thin, and white substance, terminating in the form of a crescent; the scarf-skin adheres very strongly to this part; the body of the nail is broader, thicker, and apparently of a redder colour; and the extremity is of still greater firmness. Nails increase from the root and not from their upper extremities. Their principal use is to cover and defend the ends of the fingers and toes from external injury,

and to strengthen those parts, and prevent their bending backwards when applied with force against any hard resisting body.

The foregoing sketch or outline respecting the structure and functions of the human body may, it is presumed, with the subjoined plates, be considered as an introduction to a study, that cannot fail to be interesting to young persons, who have had no previous opportunity of considering the subject. It will also, it is hoped, be considered as a proper introduction to Dr. Paley's work, on "Natural Theology," which cannot be recommended too strongly. Those who would enter farther into the subject of Anatomy, and yet who do not pursue it professionally, will find an interesting article in Nicholson's British Encyclopedia; and a still larger account, in a work entitled "The Popular Compendium of Anatomy, &c. By William Burke." To both these, as well as to the "Natural Theology," this part of our own volume stands considerably indebted. See plates on this subject at the end of the volume.

A LETTER

From a Father to his Son, on the Evidences of the Truth of the Christian Religion.

MY DEAR SON,

YOU will not be surprized, that in the present circumstances I address you in a tone more serious than usual. In the course of a few days you will quit the parental roof; and, free from the immediate restraint of a father's authority, you will enter into a situation of life in which your conduct will be necessarily left in a great degree to the guidance of your own discretion. Though I have happily no occasion to question the general excellence of your dispositions, your natural good sense will suggest to you that this is to me an anxious moment. May I indulge the hope that you participate in my feelings? Elated as you in all probability are, at the prospect of extended freedom and independence of action, I could wish you to pause for a moment before you commence your new career, and maturely to reflect upon the perils to which you will soon be exposed. The hazards to which inexperienced youths are subject on their introduction to an extensive intercourse with the world at large, constitute a subject of daily remark, and afford a copious theme to the moralists with whose writings I have endeavoured to render you familiarly acquainted. With a view of obviating these hazards, I have not only inculcated upon you the precepts of the moralists in question, and from time to time, as occasions occurred,