means confined to plants; it occurs equally in ourselves all the time; at every period of our life we have been getting through with some portion of our body; that portion acquired a certain organization, it worked for us awhile, and then being done with it, we threw it away because it was dead. Very early in the history of every individual there was a production of blood, and then followed the destruction of some of the blood corpuscles and their remains were used for various purposes. The pigment which is in the liver comes from the destroyed blood corpuscles, and it is believed that the pigment which colors the hair is derived from the same source. The blood corpuscles contain a material which when chemically elaborated reappears as the deposit which imparts to the hairs their coloration. You, of course, are all familiar with the loss of hair. It occurs to everybody, but did you ever think that it means that the hair which has lived has died, and that that hair which was a part of you has been cast off? That is what the loss of hair means to the biologist—the death of a part and the throwing away of it, and it is typical of what is going on through the body all the time. It occurs in the intestines, where the elements which serve for purposes of digestion are continually dying and being cast off. The outer skin is constantly falling off and being renewed, and that which goes is dead. In every part of the body we can find something which is dying. Death is an accompaniment of development; parts of us are passing off from the limbo of the living all the time, and the maintenance of the life of each individual of us depends partially upon the continual death going on in minute fragments of our body here and there.
Our next step in this course of lectures will carry us into the microscopic world, and with the aid of the lantern at the next lecture I shall hope to demonstrate to you a little of the microscopic structure of the body and of the general nature of the change, which exhibits itself in the body from its earliest to its latest condition. With such knowlege in our minds, we shall be able next to study some of the laws of growth. We shall gain from our microscopic information a deeper insight into some of the secrets of the changes, which age produces in the human body.
