A great part of the bile is absorbed into the blood, so that as it is absorbed into the blood of the intestines, and comes back through the portal vein to the liver, it would seem as if certain parts of the bile travelled in a circle to and from the liver. Only a small portion of the bile, more especially the colouring matter, is excreted as waste matter.

The liver is also said by some physiologists to be one of the sources of the white corpuscles of the blood. It is known that in the blood that leaves the liver a larger proportion than usual of white corpuscles exist. It is believed to be an organ in which waste red corpuscles are got rid of (because they waste, just as all the other parts of the body do), and some parts of the bile consist of substances of which these red corpuscles were composed.

You see already, from what I have told yon, that in the liver certain substances are separated from the blood, and certain substances added to it.

I will go on at once to speak of the important organs which separate the waste substances from the blood; they are called Excretory Organs, and are the lungs, the skin, and the kidneys. The Lungs I have already described to you, but I want to remind you of this, that the lungs are organs the interior of which is in connection with the external air, organs which are very highly supplied with blood, organs in which the blood is brought into almost immediate contact with the external air, being only separated from it by a fine moist membrane. The lungs separate from the blood, in the first place, waste carbon in the form of carbonic acid. Now carbon, or charcoal, is a substance that is contained in almost all our tissues, and in almost all our foods, so that it is a substance that is being continually added to the body, and has to be continually got rid of. The amount of carbon, in the form of carbonic acid, that is got rid of by the lungs of an adult in twenty-four hours is very nearly eight ounces, or half a pound. Besides carbonic acid, water, on an average about nine ounces, or very nearly half an imperial pint, is got rid of from the lungs of each individual in twenty-four hours, and. also a certain amount of foul organic matter.

The other excretory organs - the skin and the kidneys - get rid of these same substances, water, carbonic acid, and organic matter; and the kidneys, in addition, remove large quantities of mineral salts.

The Skin of the body consists of two chief layers. The first, or outer layer, goes by the name of the scarf-skin or epidermis. It is insensible, horny, not supplied with blood, dead, and consists of scales, which are continually falling off. The deeper layer is very largely supplied with blood, running, of course, in capillary vessels, and a certain amount of exudation from that is able to take place through the epidermis or scarf-skin. This is of very small importance, but of much greater importance is the fact that certain substances are separated from the blood in the true skin by means of glands. There is an enormous number of glands situated in the true skin of the body. These glands are true glands. They consist of structures around projections from the surface of the skin, and go by the name of sudoriparous or sweat glands, or perspiration glands.

Each of these glands consists of a long tube that is pushed in from the epidermis, as it were. It starts at the surface or scarf-skin, and runs through in a corkscrew-like fashion into the true skin, and is there twisted up into a ball, which contains a very large number of capillary blood-vessels.

By these sudoriparous or perspiration glands, a fluid is secreted, consisting of water having a very small quantity of salt and organic matter dissolved in it It is found also that by these glands a certain quantity of carbonic acid gas is got rid of from the blood, and that through them a small quantity of oxygen gas gets into the blood, so that you see the action of these glands is similar to the action of the lungs, only that the quantities of the substances got rid of are different. From the lungs a large quantity of carbonic acid is got rid of - from the glands a very small quantity; on the other hand, in twenty-four hours, about twice as much water is ordinarily got rid of from the perspiration glands as from the lungs - i.e., about eighteen ounces. This amount varies with the temperature, exercise taken, etc.

The number of these glands that are found in the true skin varies very much in different parts of the body, but altogether there are two and a half millions on the surface of the body. The openings of their tubes are commonly known as the pores of the skin.

There are other glands in the true skin which do not perform the functions just described.

Connected with the scarf-skin there are certain structures in different parts of the body which are peculiar varieties of the epidermis or scarf-skin: such are the nails and hairs.

In connection with the hairs there are certain little glands called sebaceous, or, if you like, little glands which secrete an oily fluid, a kind of natural grease for the hair and skin. It keeps the hair and skin constantly lubricated. I may also mention here, that attached to the roots of the hairs in the skin there are small involuntary muscles, the object of which is clearly to move the hairs. They are capable of contracting under certain very strong stimuli, and when we say that a person's hair "stands on end" when he is very much astonished or under strong excitement, it is not a fiction, but literally the fact. Any strong emotion may indirectly cause the muscular fibres to contract, and the hair to stand on end.