20 INTRODUCTION TO CYTOLOGY 



the types of organs developed depend upon the hereditary constitution 

 of the organism, their arrangement and mutual behavior are due in large 

 measure to the gradient. This is indicated by the fact that experimental 

 alterations in the metabolic rate along the axis are followed by the 

 expected abnormalities in structural development. 



As to the means by which different regions along an axis influence one 

 another, Child (1915, p. 224) adduces evidence in support of the theory 

 that the fundamental relations of polarity "depend primarily upon 

 impulses or changes of some sort transmitted from the dominant region, 

 rather than upon the transportation of chemical substances." Very 

 significant in this connection is the fact that there is a definite relation 

 between physiological gradients and electrical polarity. The dominant 

 and less active regions are respectively the negative and positive poles 

 of the living system. Where the current enters the system from the 

 exterior (negative pole), anabolic processes are promoted through 

 increased oxidation; and where it leaves (positive pole), catabolic proc- 

 esses are furthered." Alterations in electrical polarity are accompanied 

 by alterations in the mode of growth. ^^ Thus, in the opinion of Lillie 

 (1923), "bioelectric currents exert a controlling and coordinating influence 

 in normal growth processes as well as in normal stimulation." 



The Cell Theory and the Organismal Theory. — Although not of the 

 first importance to the student beginning work in cytology, the following 

 discussion is added because of its theoretical interest. 



The fact that the body of a higher organism comprises a vast number 

 of specialized parts, the cells, led many years ago to the formulation of 

 two general theories which differed in their interpretation of the relation 

 existing between the two individualities : the organism as a whole and the 

 cell. These theories are known as the cell theory and the organismal 

 theory. 



The cell theory set forth a century ago by Dutrochet, Schleiden, and 

 Schwann exerted a dominating influence upon biology throughout the 

 nineteenth century (see Chapter XXVI). The principal propositions 

 involved in the theory are summarized by Heidenhain (1907, p. 29) 

 essentially as follows: All living substance is concentrated in cells; the 

 cells of the body are all individuals of the same morphological rank; 

 the tissue cell is morphologically and physiologically an elementary 

 individual, the unit of structure and function; the body is an aggregate 

 of cells, which are its "building stones"; the action of the body is the sum 

 of the many special actions performed by collaborating cells of many 

 kinds. According to this theory, therefore, the cell is the fundamentally 

 important individual — the "primary agent of organization." In 

 ontogeny the multiplying elementary organisms, or cells, cooperate to 



17 Hering (1888), Mathews (1903), R. S. Lillie (1919, 1922, 1923). 



18 Bose (1918), Ingvar (1920), Lund (1921). See also Beutner (1933). 



