Rudolph Virchow in 1858 instituted the doctrine or theory known as "Modern Vitalism," which, in fact, was borrowed from natural scientific medicine, and distinguished from the vitalism of the previous century in that it breaks up the old vital force, which was supposed to be either distributed throughout the entire body or located in a few organs, into an indefinite number of associate vital forces working harmoniously, and assigns to them all the final elementary principles without microscopic seat. "Every animal principle has a sum of vital unities, each of which bears all the characteristics of life. The characteristics and unity of life cannot be found in any determinate{256} point of a higher organism,--e.g., in the brain,--but only in the definite, ever-recurring arrangement of each element present; hence it results that the composition of a large body amounts to a kind of social arrangement, in which each one of the movements of individual existence is dependent upon the others, but in such a way that each element has a special activity of its own, and that each, although it receives the impulse to its own activity from other parts, still itself performs its own functions." This is nothing but another way of expressing the cell-doctrine, to which many medical men are now committed, which means that all bodies are built up of cells and that each cell has a unity and a purpose of its own. In 1677 Sir Robert Hooke discovered plant-cells; later Schwann discovered animal cells and Robert Brown cell-nuclei; but it remained for Virchow to supply the gap which had risen between anatomical knowledge and medical theory; that is, to supply a "cellular pathology," since which time the cell has assumed the rôle which the fibre occupied in the theories of the seventeenth and eighteenth centuries. Time alone can decide as to the ultimate validity of this theory, which has in certain circles been most enthusiastically received. One of its weakest aspects is, perhaps, that the so-called intercellular substance plays an uncertain and unsatisfactory part. An important feature in which the cellular pathology differs from other systems, and particularly from the old humoral pathology, is in the doctrine that the blood itself is not the proper and original cause of dyscrasiæ, and probably not the cause of continuous alteration of the tissues; that these dyscrasiæ arise because the blood is not an independent structure, but dependent upon the condition of the patient in consequence of its continuous conveyance of the noxious material from all parts of the body,--the blood is, therefore, merely the medium for the production of the dyscrasia. This theory has made several peculiar, new, and symptomatic or morphological{257} forms of disease, such as leukæmia, leucocytosis, etc. Virchow also cleared up the old and obscure ideas regarding pyæmia, and proved that an absorption of pus into the blood, which the name