The clear-cut, intellectual face of Schultze (Fig. 88) is that of an admirable man with a combination of the artistic and the scientific temperaments. He was greatly interested in music from his youth up, and by the side of his microscope was his well-beloved violin. He was some time professor in the University of Halle, and in 1859 went to Bonn as professor of anatomy and director of the Anatomical Institute. His service to histology has already been spoken of (Chapter VIII). This astute observer will have an enduring fame in biological science, not only for the part he played in the development of the protoplasm idea, but also on account of other extensive labors. In 1866 he founded the leading periodical in microscopic anatomy, the _Archiv für Mikroscopische Anatomie_. This periodical was continued after the untimely death of Schultze in 1874, and to-day is one of the leading biological periodicals. It is easy, looking backward, to observe that the period between 1840 and 1860 was a very important one for modern biology. Many new ideas were coming into existence, but through this period we can trace distinctly, step by step, the gradual approach to the idea that protoplasm, the living substance of organism, is practically the same in plants and in animals. Let us picture to ourselves the consequences of the acceptance of this idea. Now for the first time physiologists began to have their attention directed to the actually living substance; now for the first time they saw clearly that all future progress was to be made by studying this living substance--the seat of vital activity. This was the beginning of modern biology. Protoplasm is the particular object of study for the biologist. To observe its properties, to determine how it behaves under different conditions, how it responds to stimuli and natural agencies, to discover the relation of the internal changes to the outside agencies: these, which constitute the fundamental ideas of biology, were for the first time brought directly to the attention of the naturalist, about the year 1860--that epoch-making time when appeared Darwin's _Origin of Species_ and Spencer's _First Principles_. CHAPTER XIII THE WORK OF PASTEUR, KOCH, AND OTHERS The knowledge of bacteria, those minutest forms of life, has exerted a profound influence upon the development of general biology. There are many questions relating to bacteria that are strictly medical, but other phases of their life and activities are broadly biological, and some of those broader aspects will next be brought under consideration.