In reality, instead of all Protoplasm being the same, the differences are infinite. Particles from different sources may be indistinguishable by the microscope or by any test that chemistry can apply, but this only increases the mystery of their nature, for each has its own functions and will perform no others. The Protoplasm of a plant will do what that of an animal, seemingly identical, cannot do. That of a fish will convert the same nutriment into quite a different formation from that of a man. It is no doubt true that a particle of fungoid differs in no appreciable physical respect from one of human protoplasm, yet the former will never emerge from the fate of the humble mushroom, while the other may be instinct with the thoughts of a Prime Minister.[99] As Mr. Stirling sums up the matter:[100] There is nerve-protoplasm, brain-protoplasm, bone-protoplasm, muscle-protoplasm, and protoplasm of all the other tissues, no one of which but produces only its own kind, and is uninterchangeable with the rest. Lastly, we have the overwhelming fact that there is the infinitely different protoplasm of the various infinitely different plants and animals, in each of which its own protoplasm, as in the case of the various tissues, but produces its own kind, and is uninterchangeable with that of the rest. It thus appears that the character of Protoplasm, far from making it easier to conceive the mechanical production of living things, does but immensely aggravate the difficulty. As Sir William Thiselton-Dyer avows: "I do not see even the beginning of a materialistic theory of protoplasm." And Haeckel's idea that we shall succeed in creating organic life does not commend itself to such an authority as Sir Henry Roscoe: It is true [he says][101] that there are those who profess to foresee that the day will arise when the chemist, by a succession of constructive efforts may pass beyond albumen, and gather the elements of lifeless matter into a living structure. Whatever may be said of this from other standpoints, the chemist can only say that at present no such problem lies within his province. Protoplasm, with which the simplest manifestations of life are associated, is not a compound, but a structure built up of compounds. The chemist may successfully synthesize any of its component compounds, but he has no more reason to look forward to the synthetic production of the structure than to imagine that the synthesis of gallic acid leads to the artificial production of gall-nuts. And M. de Quatrefages thus sums up the conclusions at which he arrives from minute study of the lowest forms of life:[102]