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.