But here will challenge some twentieth-century _Gradgrind_: "This is all very pretty from the point of view of abstract science, but what is the practical value of it? The discovery of the plasmodium and its peculiarities has merely shown us the how and the why of a fact that we had known well and utilized for centuries, namely, that quinine will cure malaria." Just listen to what follows. The story of the plasmodium is one of the most beautiful illustrations of the fact that there is no such thing as useless or unpractical knowledge. The only thing that makes any knowledge unpractical is our more or less temporary ignorance of how to apply it. The first question which instantly raised itself was, "How did the plasmodium get into human blood?" The very sickle-shape of the plasmodium turned itself into an interrogation mark. The first clew that was given was the new and interesting one that this organism was a new departure in the germ line in that it was an animal, instead of a plant, like all the other hitherto known bacilli, bacteria, and other disease-germs. It may be remarked in passing that its discovery had another incidental practical lesson of enormous value, and that was that it paved the way for the identification of a whole class of animal parasites causing infectious diseases, which already includes the organisms of Texas fever in cattle, dourine in horses, the _tsetse_ fly disease, the dreaded sleeping sickness, and finally such world-renowned plagues as syphilis and perhaps smallpox.