too, the glands have cells which are especially capable of elaborating chemical substances which, when the}-are poured out, accomplish the work of digestion, for instance. But these cells are likewise alive in all their parts. They have all the fundamental vital properties, but there is this tremendous exaggeration of the one faculty, and that involves an alteration so great in the protoplasm that we can see it with the microscope; the microscope affords us a perfect demonstration of differentiation, which we can correlate with the function.
The primary object, therefore, of all differentiation is physiological. The higher organism, with its complex physiological relations, is something really higher in structure than the lower organism. The term "higher" in biology implies a much more complex interrelation of the parts, a much more complex relation of the organism to the outside world; and above all it implies in the highest animals a complex intelligence of which only a rudimentary prophecy exists in the lowest forms of life, possibly scarcely more than a mere sensation. We owe then to differentiation our faculties, which we prize. It is the result of differentiation that I am able to address you and present before you the thoughts which have been accumulated as the result of the studies of many years. It is a result of differentiation that you have such, parts that you not only hear the actual sound of my voice, but interpret—at least I hope so—the meaning of my words and can understand the ideas which I am endeavoring to present to you. If you carry away something from these lectures, and recall it at some future time, that also will be a result of the differentiation of structure; for every one of you started as a minute germ, consisting of protoplasm with a nucleus, and entirely without any differentiation; and by a process so complex that the mystery of it escapes entirely all our powers of analysis, those parts which you have have been slowly and secretly fashioned. We have approached one of the fundamental problems of existence. When we talk of differentiation, we talk of the endowments which bring us into relation with the external world—into relations with our kind, and which make our internal life so complex, a complexity which in itself is a great problem. We touch here the fundamental mysteries of existence; we are hovering upon the outskirts of our human conceptions. We are not yet able to press beyond. But perhaps the time may come when the limit to which I can now bring you will be moved farther back, and some of the things which are at the present time utterly mysterious and incomprehensible to us will be comprehended and be explicable to you.
The increase of the protoplasm is then, as we have clearly seen from the pictures, the mark both of advancing organization and of advancing age. It is certainly somewhat paradoxical to assert that the increase of the protoplasm is a sign of old age, a sign of senescence, since protoplasm is the physical basis of life. It undoubtedly is such,
