It would be well worth while to stop to consider how much the various branches of engineering owe to pure mathematics and pure physics; or to relate the rise of numerous great industries that have grown out of the theoretical study of chemistry. Where would be our electric lighting and transportation but for the explanations of Franklin, Volta and Faraday? But I will limit myself to the practical value of pure science as exemplified by a particular one, biology. In making this restriction I should add that history tells how each of the pure sciences has led to useful ends, so that biology is but one of several cooperating sisters, each making her contribution to greater human happiness.
Biology has to explain the nature of living energies in treating of animals and plants and of man himself. Biology has to interpret processes, and this it attempts to do in a variety of ways according to the nature of the problem, the material and the bias of the thinker. Biology has to some extent grown up side by side with medicine; each helped the other in the days of their beginnings, and for that reason we may first treat its practical bearings to medicine.
In the seventeenth century the microscope came into use and it opened up, in the hands of Leeuwenhoek and Schwammerdamm, a wealth of unexpected detail. Leeuwenhoek exhibited his dissection of an ant to the delighted eyes of a king; since that time the tastes of royalty seem to have deteriorated. But such discoveries in the finer details of anatomy only presented new problems. The partial explanation came in 1838 with Schleiden and the following year with Schwann, who stated that animals and plants are built up of definite living units, the cells; that such units compose the tissues that had been determined by the physiologist Bichat, and that the organs are composed of definite layers of cells. The simplest animals, what we now call the Protozoa, were shown by Dujardin to be each composed of only a single cell. We define a cell as a particular mass of living substance regulated by a particular center, the nucleus. This view was strengthened by the notable researches of particularly von Kölliker and Max Schultze, and so gradually extended to all animals and plants as well as to the human body. Eduard van Beneden later finally settled the fact that the egg, the beginning of each many-celled animal, is itself a single cell. Thus biologists have come to concentrate their attention upon cell activities, and this cell unit has proved as fruitful in biology as the atom in chemistry, though the cell is something vastly more complex than many atoms. Now there grew up with this new doctrine Rudolf Virchow, the great master of the study of disease, and he it was who by placing the study of disease upon the cellular basis, by tracing diseased conditions to particular cells, laid the rational foundation of one branch of modern medicine. The investigation of the