The returning venous blood reaches the right auricle; when the latter is filled to its capacity its walls contract and expel the blood through an opening into the right ventricle; this in turn contracts and forces the blood through the pulmonary artery into the lungs (there to undergo a process which we shall consider presently). After the processes of the lungs have been performed, the blood is forced back into the left auricle of the heart, which in turn forces it into the left ventricle. The left ventricle then forces the blood out into the arteries through the aorta, which latter is the largest artery of the system.

The arterial system carries forward the blood-current, first through the main arteries and then through the divisions and subdivisions thereof, ending in the tiny hair-like capillaries which reach to every cell and cell group in the body. The blood having given up such part of its nourishment as is needed at the moment, and having transferred a tiny particle of oxygen to such points where it is needed, then starts on its return journey to the lungs, this time taking the route of the veins, for it is now venous blood, dark, dull, lacking in oxygen, and filled with impurities. It starts back first through the capillaries of the venous system, then passing on to the smaller veins, and then to the larger, and then to the main veins which pour it into the right auricle (as previously stated), from which it is passed via the right ventricle and the pulmonary artery into the lungs, there to be purified and oxygenated.

To many it seems strange to include the lungs when considering the subject of the circulation of the blood; but in a moment we shall see that the sole offices of the lungs are the performance of the work of cleansing and oxygenating the blood-without this there would be no need of lungs at all. Yet so ignorant is the general person of the principles of physiology that the lungs seem utterly devoid of any connection with the blood, and from any functions to be performed in the direction indicated. There is great need for public instruction on this point-for knowledge here certainly spells H-e-a-l-t-h to mankind.

The Lungs are two in number, and are located in the upper part of the trunk, in that part of the body commonly called "the chest." They are separated from each other by the heart, and its great blood-vessels, and the larger air tubes. The trachea, or windpipe, conveys the inspired air to the lungs; at its lower end" it divides into the bronchial tubes which enter the lungs. The bronchial tubes then divide and subdivide into smaller tubes, like the branches and twigs of a tree, until they terminate into tiny lobules, or oval sacs or bags. These lobules or air-spaces in the lungs are very small and very numerous; it is estimated that there are many millions of them in each lung. It has been estimated that if these air cells of the lungs were spread out on a plane surface they would extend over an area of nearly fifteen thousand square feet.

These tiny air-cells are enmeshed in an intricate network of tiny capillaries of the circulatory system, which are filled with venous blood just returned from the various parts of the system to the lungs, there to be purified and oxygenated. It is estimated that about 35,000 pints of blood traverse or pass through these capillaries each twenty-four hours, the blood corpuscles passing in single file through these tiny capillary canals, each being exposed to a tiny particle of air on each side of the canals.

When the blood corpuscle comes in contact with the air in the lungs, as just stated, the oxygen in the air penetrates the coating of the coverings, and, coming into direct contact with the blood, oxygenation and a process of chemical combustion takes place. In this process the oxygen "burns up" the filthy waste matter in the venous blood and converts it into carbonic-acid gas which is then thrown out of the lungs in the expiring breath. And, at the same time the blood takes up tiny particles of oxygen which it carries to all parts of the system, where it is used in certain important processes in connection with the cells and tissues-it serving to strengthen and invigorate, renovate and repair, every cell and tissue. Arterial blood carries with it about twenty-five per cent of pure oxygen.

Not only does the oxygen in the blood perform the office above mentioned, but it also materially aids in certain processes of digestion which depends upon a proper oxygenation. The combustion arising from the contact of the oxygen with the waste substances also generates heat, and equalizes the temperature of the body.

In addition to the system cf blood-circulation, there is another very important system existing and operating in co-operation with the former. This secondary system is called the Lymphatic System. Lymph closely resembles Blood in its composition. It is composed of some of the ingredients of the blood which have exuded from the walls of the blood-vessels, and also of some of the waste materials of the system which require "making over." The lymphatic system attends to this repair work, and also several other functions of the system. The renovated waste-material is passed once more into the blood, there to be used by the system. The lymph circulates in thin, very delicate tubes, which are invisible to the unaided human eye- they may be injected with quicksilver, however, and thus made visible. These lymphatic tubes empty into several of the large veins, the lymph mingling with the returning venous blood, and thus reaching the lungs and heart in due course. Certain portions of the food-nourishment reach the lymphatic system from the intestines, and there undergo certain transforming processes before entering the blood-supply proper.

So, we see the importance of the blood in the work of body-building and body-maintaining. The blood in one's body constitutes one-tenth of his entire weight. Of this amount about one-quarter is distributed in the heart, lungs, large arteries and veins; about one-quarter in the liver; about one-quarter in the muscles; the remaining one-quarter being distributed among the other organs and tissues; the brain utilizing about one-fifth of the entire quantity of blood in the system.

It is seen without argument that the general health of a person depends materially upon his supply of blood being adequate, rich, and sufficiently well oxygenated. The richness of the blood depends, of course, upon the work of the organs of nutrition; its oxygenation depends upon the work of the lungs; and its normal action upon the work of the heart and the arterial and venous system. All of these organs are amenable to mental treatment along the general lines laid down in these lessons.

The lungs are quite receptive to mental treatment, and respond by displaying greater strength and activity, particularly when aided by the cultivation of the habit of proper breathing, which habit most persons have lost. The heart and the 4 arterial and venous systems respond readily to mental treatment. So true is this that strong positive mental suggestion will increase the circulation to any one part to which the attention and treatment is directed-this may be proved by actual experiment. The action of the heart has been found to respond to properly directed suggestion-this also is capable of being proved by experiment, though one should not experiment idly with this organ. The heart is the most intelligent and sensitive of all the organs of the body. It responds to loving, careful suggestions and advice-but must never be driven or abused.