SECTION II. 

 CELLULAR PHYSICS. 



I. THE PHYSICAL PEOCESSES IN CELLS. 



As the tissues and organs of the animal body originate in ceils, we 

 should expect that the functions of the higher organisms, which we know 

 to be identical with those of the most elementary forms of life, would to 

 a certain extent be accomplished by the same general processes. We 

 have already divided the functions of animal life into the vegetative, or 

 nutritive, functions and the functions of relation, and have called atten- 

 tion to the attempt which has been made to reduce the working of these 

 processes to physical and chemical laws. Although in many points this 

 endeavor fails, the operation of the ordinary physical and chemical laws 

 serves to explain many of the complex phenomena of animal life. This 

 is especially seen in the maintenance of the nutrition of the organism. 



That cells may retain a nutritive balance it is requisite, in the first 

 place, that they be .supplied with a proper pabulum, which must pass 

 from the exterior to the interior of the cells. We have found that the 

 typical cell is surrounded by a homogeneous or striated membrane, 

 which, like all other organic tissues, contains a large amount of water 

 closely associated with the ultimate molecules of which that membrane 

 is made up. Hence, the cell-membrane may be regarded as a porous 

 partition whose pores are filled with water, and which separates the 

 cell-contents from the surrounding media. These media may be either 

 gaseous, as the atmosphere ; fluid, like the lymph and blood in higher 

 animal forms, or water in aquatic forms of life; or semi-fluid, like the 

 more or less solid intercellular substance. 



This passage of nutriment from the exterior to the interior of cells 

 is mainly accomplished b}^ purely physical means, not only in simple 

 unicellular organisms but also in higher forms of life, where digestion, 

 or the preparation of food for absorption, has for its object the reduc- 

 tion of food into such forms that the operation of the physical laws of 

 imbibition, capillarity, filtration, diffusion, and osmosis, aided perhaps 

 by chemical affinity, will be sufficient to enable the nutritive matters to 

 pass to the interior of cells. 



When once in the interior of the cells the raw food-products must 

 be transformed into protoplasm similar to that of which the cell-contents 



(37) 



