Although the discovery of the circulation of the blood is of comparatively recent date, yet from the earliest times thoughtful men have recognized the all-important offices of thè blood in the vital processes. They have realized that in some mysterious way physical life and health is closely bound up with the blood supply and the purity thereof. This thought is expressed in countless aphorisms, of which the one quoted at the head of this lesson ("The Blood is the Life") is a typical example.

In view of the facts of the case, it is amazing that the average person has but the slightest conception of the offices of the blood, and the processes of the circulation of the blood. The average man does not grasp the idea that the blood is filled with the nourishment extracted from the food, and that the circulation of the blood is largely concerned with the distribution of this nourishment. Instead, he has a general hazy idea that the nourishment is "soaked up" by the system from the stomach in some unknown and mysterious way. He realizes that his blood is an important item of his physical well-being, and that if it is weak, or if he loses it, he weakens or dies-but this is about as far as his thought of the subject extends.

I have found it advisable to inform patients on this point, because when they grasp the idea their minds seem to take up the suggestion more clearly, and they unconsciously co-operate with the efforts of the practitioner to bring about improved nutrition of all parts of the body. The suggestion of "rich red blood, flowing to all parts of the body, building up and strengthening it, repairing and creating it anew," is one of the greatest value in many cases. The patient easily, and involuntarily, makes a mental picture of the desired condition, which, of course, is then objectified in his physical condition according to the rule that "mental ideas take form in physical conditions."

Let us then carefully study the processes of the circulation of the blood, and the offices and functions of the blood, that we may hold the right kind of mental pictures ourselves, and thus be able to convey the same to the mind of the patient in our work of treatment.

The Blood is the red fluid which circulates through the arteries and veins of man and the higher animals. It is formed from the Chyle and Lymph when these substances are subjected to the action of the oxygen taken into the lungs by the process of inspiration. It is the general material from which all of the secretions of the body are derived. In the blood current is also carried away from the different parts of the body various noxious debris and waste products of the system, which are thus carried to the crematory of the lungs, there to be burned up by the oxygen therein, and then eliminated from the system in the form of carbonic-acid gas.

Blood has a salty taste, and when fresh it has a peculiar odor. It is composed of about seventy-eight per cent of water; about six or seven per cent of albumen; about thirteen per cent of coloring matter; and a small percentage each of fibrine, crystallizable fat, fluid fat, and various mineral chemicals such as sodium and potassium chlorides, carbonates, phosphates, and sulphates, and calcium and magnesium carbonates, phosphates of calcium magnesium and iron, ferric oxide, etc. Under microscopic examination it is seen as a colorless liquid with many minute round red blood corpuscles floating in it, and a smaller number of larger discs called "white corpuscles" moving in its substance. The idea of the real nature of the blood may be grasped from the following statement of an authority on physiology who says: "The blood is the immediate pabulum, or nourishment and sustenance,, of the tissues. Its composition is practically identical with that of the tissues; in fact, it is really liquid flesh."

The vessels which conduct the blood outward from the heart are known as Arteries; and those which conduct it back to the heart are known as Veins. The blood in the arteries (called "arterial blood") is of a bright red color, while that in the veins (called "venous blood") is of a dark, dull, blackish-purple color. Arterial blood is highly charged with oxygen; venous blood is deoxidized, or lacking in oxygen. We shall see the reason for this difference in the two kinds of blood, or rather the two conditions of the blood (for it is really all the same blood appearing in two conditions or states) when we now study the office of the blood, and the processes of the circulation thereof.

The nourishment of the food is taken into the blood by absorption from the organs of digestion, as we have seen in the lesson on these processes. It reaches the heart and is then sent forward to all parts of the body in the current of rich, red arterial blood which has just been freshly oxygenated by the lungs, as we shall see presently. It is carried to all parts of the body, where it is eagerly taken up by the various class and tissues, and by them is converted into new cell-substance, and tissue-substance, and built into flesh, muscle, and tissue in general. The body needs this new material in order to replace that which has broken down and been discarded; and also to repair the remaining tissue-substance.

The blood returning to the heart in the condition of dark, dirty venous blood carries with it the garbage and debris of the system, the particles of broken down cells and tissue, and other impurities of the system, which, if left in the system, would poison it. This debris is bound for the crematory of the lungs, where it is burned up by the oxygen inspired in the act of breathing, and is then cast forth in the form of carbonic-acid gas.

Before proceeding to a consideration of the process of the lungs, however, let us stop for a moment to view that wonderful instrument, the Heart. The Heart is a hollow, pear-shaped organ, about the size of an average clenched fist. It is situated on the left-hand side of the body, between the two lungs. It is divided into lour compartments, of which the two upper are called auricles, and the two lower called ventricles* The auricles have veins opening into them; the ventricles have arteries arising from them.