Page:The Harveian oration 1903.djvu/44

 as they were their origins. Hence we call them the living elements, and hence we regard them as the anatomical basis of all biological analysis, whether it has a physiological or a pathological object in view. The cells are composed of organic chemical substances, which are not themselves alive, but the mechanical arrangement of which determines the direction and power of their activity."

Before proceeding to consider the next and chemical stage of structure it would be well shortly to indicate some of the living phenomena which have either already received or still await their explanation in the intimate histology of the cell. Most important of these is contractility, whether this be manifested as irregular amceboid movements, the rhythmic wavings of cilia, or the orderly and more highly differentiated contraction of muscular tissue. The ebb and flow of the more diffluent portions into and out of the reticulum of the spongio-plasm—the "streaming" as it has been termed—is a step towards explaining—apart altogether from the attempt to express protoplasmic movement in terms of inorganic phenomena, such as has been done—those alternate contractions and expansions of the bioplasm due to reciprocal rearrangements of its particles, which constitute one of the