Now you must fancy from that that there must be a great many of them, and that they must be very small; they are about the 3200th part of an inch across; 3200 would lie along an inch. That, however, does not give you much idea of their size. I will give you a better idea, not so much of their size as of the number of them that are in the blood. Suppose I take a cubic inch of blood, how many do you think there would be in it? there would be seventy thousand millions-that seems very astonishing, but still it does not give you the least idea how many there are. I will give you an idea in this way. Suppose that you were to begin counting, and go on day and night without any intermission, and that you were to count one hundred a minute, it would take you, making allowance for leap years, just 1331 years to count the red corpuscles in one cubic inch of blood; so that if William the Conqueror had begun counting when he came over to England, and had gone on day and night at that rate, he would not now have got through two-thirds of the number contained in a cubic inch of blood.

Besides these there is another lot of corpuscles called white corpuscles, which are larger than the red corpuscles, and are irregular in shape; they have a peculiarity in that they have one or more smaller bodies inside them, and I may tell you that it is generally believed that the red ones are developed from these small bodies that are inside the white ones. They are not nearly so numerous as the red corpuscles, but in the proportion of something like three or four to 1000 red ones. Where they come from we shall see hereafter.

The blood when it is run out of the blood-vessels does not remain liquid, but a thick clot forms in it; this is called coagulation of the blood; the importance of it to us is that when cut or abraded surfaces bleed, clots form, and plug up the cut ends of the capillary vessels, so helping to stop the bleeding.

There is another set of vessels in the body besides the blood-vessels, and these vessels do not form a closed circulatory system of tubes like the blood-vessels. They begin almost everywhere in the tissues of the body as thin fine vessels, and they run together into solid-looking bodies that are called glands. These vessels contain a fluid called lymph, because it is like water, and the vessels themselves, because they contain this fluid, are called lymphatic vessels, and the glands lymphatic glands.

These glands are more numerous in some parts of the body than in others; there are a great many about the intestines, and a good many in the neck and under the arms. The lymphatic vessels empty into cavities in the glands, and then other rather larger vessels start away from the other side of these bodies, and run on until they come to some more of them, and so these glands are joined together by the lymphatic vessels running from one to the other. They are like veins in that they have valves in them, which only allow the fluid to go one way, viz. from the smaller vessels towards the larger ones. The lymphatics from the lower part of the body all run together into a receptacle placed against the bodies of the lumbar vertebrae. This receptacle goes by the name of the receptacle of the chyle ; it is connected with a tube about the size of a goose quill running up close to the left side of the bodies of the dorsal vertebrae into the neck, and emptying itself into the junction of the vein from the left arm and the great vein from the left side of the head (called the jugular vein), and where it empties itself into the veins there is a valve, which is so arranged that no blood can go out of the veins into this tube, which is called the thoracic duct, but the fluid that is in that duct can go into the blood that is in the veins-that is the course of the lymphatic vessels of the lower part of the body, and of the left side of the chest and head and left arm. But the lymphatics of the right arm and right side of the head and neck, and the upper part of the right side of the chest, do not go into the thoracic duct at all, but empty themselves into the veins in a corresponding place on the other side; so that ultimately all the lymph that comes from all the tissues of the body gets into the great veins which run into the upper vena cava, and so into the right auricle of the heart.

Now the lymphatics of the small intestines have, especially after the digestion of food, a fluid in them which is not like water; but, on the contrary, it is white like milk, and for the same reason that milk is white, namely, that it has a great quantity of fat suspended in it; this white fluid goes by the name of chyle, and the lymphatics of the small intestines, because they contain this milky fluid, are called the lacteals, though they do not differ from the lymphatics in any other part of the body, except that they contain this white chyle, and they of course go through a series of glands into the receptacle of chyle, and so the old anatomists called that vessel the receptacle of the chyle, although it also receives the lymph from the greater part of the body.

The lymph in the lymphatic vessels is a watery fluid containing a certain small quantity of solid matter in solution; the chyle is a milky fluid something like lymph, only containing a large quantity of fat in suspension, and rather more solid matter in solution, and both of these fluids, like the blood, are capable of forming clots under certain circumstances. Both in the lymph and in the chyle there are corpuscles exactly like the white corpuscles of the blood, and these two fluids are continually going into the blood, so that there is no doubt that the white corpuscles in the blood are identical with the white corpuscles in the lymph and chyle. There is very little doubt that the lymphatic glands through which these fluids go, together with some other bodies about which I shall speak farther on, have the manufacture of the white corpuscles of the blood for their office.

Before leaving this, let us consider of what the blood in the right side of the heart consists, and where it comes from. I have described all the places that it comes from but one, and I will tell you of that one as we go on. This is the blood that goes into the right auricle of the heart, through the two great veins, from all the parts of the body. Suppose we take these two veins one at a time. The blood that comes in by the vena cava inferior is the blood from the lower part of the body. It contains the blood that has gone through the portal circulation in the liver, and has undergone very remarkable changes. Most of this blood has come from the digestive organs. It contains also the blood not yet mentioned, viz. that which comes from the kidneys, which has undergone certain important changes in the kidneys. That is what the inferior vena cava brings into the heart. The superior vena cava brings the blood from the upper part of the body, the lymph that has come in by the thoracic duct on the left side, and lymphatic ducts on the right side, and the chyle which has come from the lacteals through the thoracic duct. So you see that the right side of the heart contains a very curious and complex mixture.