The importance of this newly formulated doctrine it is difficult to appreciate. Here, in protoplasm had been apparently found the foundation of living phenomena. Here was a substance universally present in animals and plants, simple and uniform--a substance always present in living parts and disappearing with death. It was the simplest thing that had life, and indeed the only thing that had life, for there is no life outside of cells and protoplasm. But simple as it was it had all the fundamental properties of living things--irritability, contractibility, assimilation, and reproduction. It was a compound which seemingly deserved the name of "_physical basis of life_", which was soon given to it by Huxley. With this conception of protoplasm as the physical basis of life the problems connected with the study of life became more simplified. In order to study the nature of life it was no longer necessary to study the confusing mass of complex organs disclosed to us by animals and plants, or even the somewhat less confusing structures shown by individual cells. Even the simple cell has several separate parts capable of undergoing great modifications in different types of animals. This confusion now appeared to vanish, for only _one_ thing was found to be alive, and that was apparently very simple. But that substance exhibited all the properties of life. It moved, it could grow, and reproduce itself, so that it was necessary only to explain this substance and life would be explained.