Page:The Harveian oration 1903.djvu/55

THE HARVEIAN ORATION, 1903

49

in such external conditions as are commonly comprised in that expression. 1 The behaviour of cell to cell, their mutual interactions — cytotaxis — and their physiological resistances the one to another will have to be taken into account in forming any thorough conception of the totality of life whether healthy or diseased that an organism presents, and the understanding of such problems cannot be attained until the finite structure of the material concerned be rendered plain, or be assumed with such justification as those concepts underlying physico-chemical action at present furnish. 2

1 As illustrating these environmental relationships may be mentioned the various forms of taxis or tropism whereby the direction of the movements exhibited by living protoplasm may be influenced. The best known of these is “ chemotaxis” as met with in connection with some states of leucocytosis, but it is probable that other forms of taxis caused by pressure, gravity, heat and light also prevail. “ The spermatozoon seeks the ovum, and almost everywhere in the living world is led in the right path by the chemotactic action which the metabolic products of the egg-cell exert upon the freely moving sperm- cell. . . . Every species of spermatozoon is chemotactic to the specific substances that characterise the ovum of the correspond- species” (Verworn, General Physiology ). The effect also of these external agencies, as well as others like moisture and the density of the surrounding medium on the nutritional activity and on the power of reproduction as well as on the motility of the simplest organism has been experimentally demonstrated ; suggesting a chemical complexity of proto- plasmic structure which is open to disturbance by the external world.

2 As bearing upon these and like questions a very large body of experimental evidence exists to show that there are great

D