64 BIOLOGICAL LECTURES. 



This remarkable resemblance of the physical behavior of 

 semi-fluid living protoplasm to that of semi-fluid dead matter 

 of certain kinds, such as the oils, has led me to apply the term 

 cytopJiysics to the study of the physical properties of the 

 substance of the cell. The convenient terms cytostatics and 

 cytokinetics very naturally follow from a consideration of 

 the contrasted states of rest and activity presented by the 

 "living" cellular unit of organization. The cytostatic state 

 will be one in which no visible physical activity, other than 

 its secular metabolism, will characterize the cell, during which 

 time, also, the parts of its substance will be in a condition of 

 statical equilibrium in respect to each other, and the cell will, 

 so long as this equilibrium lasts, maintain a constant configu- 

 ration. The cytokinetic state, on the other hand, is one in 

 which the visible or invisible parts of the cell are undergoing 

 a displacement in respect to each other, as a consequence of 

 which the cell as a whole will manifest changes of configuration. 



Free and interfacial surface-tension is probably the most 

 important factor in determining the shapes of cells, since 

 there is associated with it, in multicellular organisms, a com- 

 plicated series of definite and constant space relations and 

 reciprocal interactions, as respects the cells of definite tissue- 

 tracts, that grow out of the very conditions of combination of 

 those tracts. Still more important, perhaps, are the incessant 

 unequal disturbances of surface-tension, due to metabolic 

 changes, at different points on the surfaces of cellular masses 

 of plasma a fact beautifully illustrated by the proteus ani- 

 malcule, Amoeba proteus. Differences of surface-tension are 

 thus developed at different points and times coexistently and 

 consecutively which lead to the assumption of the most diverse 

 and inconstant shapes by the bodies of these lowly organisms. 

 Such differences of surface-tension are, however, themselves 

 caused by chemical and molecular transformations at definite, 

 but previously unspecifiable, points at or near the surface of 

 the mass of plasma. These processes are, therefore, ultimately 

 to be associated with molecular or chemical transformations, 

 the production of heat, the disintegration and integration of 

 living matter. 



