The Regulation of Size as Illustrated in Unicellular Organisms

Regulation of Size in Unicellular Organisms organism is confined is invisible, for its boundaries and its skeleton are also changing. It is independent of any particular structural constituent and maintains its individuality in a medium composed of the same sub- stances as itself. Driesch ('98) suggested that the ac- curacy with which size is controlled by metabolizing organisms proved the presence of a sort of regulation which could not be performed in the absence of special vital properties. Regulation. The concrete resultant of the various processes which produce the constancy of size in an organism, and among organisms, is not unique. Every characteristic of a living being represents the manifes- tation of similar regulations. Each specific structure, each mode of physiological response, each activity, is a product of accurately measured functions. But the regulation of size is certainly as universal as, and per- CHAPTER II RATES OF GROWTH OF INDIVIDUALSTt is difficult to compare with one another the sizes --of different individuals, until the changes of size which a single individual undergoes have been recog- nized. There is a progressive increase of mass in the normal life of each individual; this is properly termed growth. Ordinarily between one fission and the next, in the course of vegetative generations, materials are assimilated and size is increased. The rate at which this increase occurs has been studied most extensively in Paramecium. 1. 'In bacteria: Barber ('08), M'Kendrick and Pai ('11), Penfold ('14), Chesney ('16). In yeasts: Slator ('13, '21), Clark ('22), Peskett ('24, '25, '-«" -S 3 3 SJ O u u "O sjnoqui uoijpaauaʲo uoflejnQ