CHAPTER III 

 PHYSIOLOGY OF CELLS 



Physiology treats of the functions or activities of living matter, 

 that is, of the processes that are going on in the living substance, the 

 part that each structure plays in the life of the organism, and the manner 

 in which the organism as a whole lives and responds to the conditions 

 of its environment. The general field of physiology may be variously 

 subdivided, but the scheme followed in this book divides the subject 

 into two parts, namely, physiology of the cell, and physiology of organs. 

 Cell physiology, to which the present discussion is devoted, treats of 

 the processes fundamental to all living matter, and since living matter, 

 or protoplasm, is always arranged in the form of cells which occur singly 

 or in aggregates a discussion of the functional relations of the parts of the 

 cell to each other is included. 



Physical and Chemical Processes of Living Matter. — Physiology is 

 coming to depend more and more upon a knowledge of physics and 

 chemistry for the solution of its problems. For this reason some of the 

 topics usually studied in connection with those sciences are introduced 

 here. These topics include diffusion, osmosis, the behavior of isotonic 

 or isosmotic solutions, and the properties of true solutions and colloidal 

 solutions. 



Diffusion. — If two or more gases are placed in a container the mole- 

 cules of each gas rapidly disperse. This dispersion continues until each 

 gas reaches the limits of the container and becomes evenly distributed 

 within the enclosed space. This action takes place without regard to the 

 force of gravitation. The phenomenon of dispersion of the molecules 

 of one substance among those of another substance is called diffusion. 



If a crystal of common salt is dropped into water, minute particles 

 of the salt separate from the crystal and, either as molecules or as ions into 

 which molecules may divide, disperse until they are evenly distributed 

 throughout the water. This also is diffusion. If a Ughter liquid that is 

 miscible with a heavier liquid is poured over the heavier hquid, care 

 being taken not to mix them during pouring, particles of the heavier 

 liquid notwithstanding its greater weight will rise into the lighter until 

 there will be a homogeneous mixture of the particles of the two liquids. 

 This process again is diffusion. The rate of diffusion of gases into each 

 other is rapid, but that of a solid into a liquid or of a liquid into a liquid 

 is much slower. Even particles of some solids which have been brought 



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