78 



THE CELL AND PROTOPLASM 



figuration. This occurs at all levels, and 

 may concern electrons, atoms, molecules, 

 cells or individual organisms. No particle 

 or unit can be wholly understood or its 

 behavior predicted unless its reactions with 

 others are taken into consideration. The 

 cell theory of the organism concerns, then, 

 not only the cells as independent units but 

 also their structural and functional rela- 

 tions to each other. 



Whitman's notable essay on ''The In- 

 adequacy of the Cell Theory of Develop- 

 ment" (1893) is often cited as opposed to 

 the cell concept of the organism. How- 

 ever, this paper is in essence a plea for 

 the recognition of a microstructure as the 

 basis of organization, and is in no sense 

 the negation of the cell as a living unit, 

 although "cellular interaction" as an ex- 

 planation of formative processes, is sum- 

 marily dismissed as a term of reference. 

 "If the formative processes," says Whit- 

 man^ "cannot be referred to cell-division, 

 to what can they be referred? To cellular 

 interaction? That would only be offering 

 a misleading name for what we cannot ex- 

 plain; and such an answer is not simply 

 worthless, but positively mischievous, if it 

 put us on the wrong track. Loeb 's experi- 

 ments in heterogenesis [heteromorphosis?] 

 furnish a refutation of the interactive 

 theory. The answer to our question may 

 be difficult to find, but we may be quite 

 certain that when found it will recognize 

 the regenerative and formative power as 

 one and the same thing throughout the 

 organic world. It will find, as Wiesner 

 has so well insisted, a common basis for 

 every grade of organization, and it will 

 abolish those fictitious distinctions we are 

 accustomed to make between the formative 

 processes of the unicellular and multicellu- 

 lar organisms. It will find the secret of 

 organization, growth, development, not in 

 cell-formation, but in those ultimate ele- 

 ments of living matter, for which idiosomes 

 seems to me an appropriate name." 



The cell theory may be subjected to 

 various experimental tests of its adequacy, 

 many of which have been devised since 

 2 Op. cit., p. 657. 



Whitman wrote his essay. In the sense of 

 those who emphasize "organization" as 

 the chief characteristic of living creatures, 

 "inadequacy" may be measured to a lim- 

 ited extent by the differences in behavior 

 between cells associated in the organism 

 and those acting alone or in small groups. 

 This has been done by means of tissue cul- 

 ture and other types of isolation, including 

 separation of blastomeres. A cell from 

 the neural tube of an embryo, isolated in 

 a suitable medium, forms a nerve fiber, 

 and a presumptive heart cell may develop 

 striations and beat rhythmically by itself 

 (Burrows, 1912) . However, the nerve fiber 

 does not function as such without connec- 

 tions, and the heart muscle cell does not 

 form an organ that pumps blood. On the 

 other hand isolated blastomeres may give 

 rise to a whole organism. Thus a cell, 

 when isolated, may do either more or less 

 than it would presumably have done if 

 left in normal relations to its associated 

 elements. 



That isolated cells often achieve so little 

 is no indication of limitation in what they 

 can do, since the conditions under which 

 they are isolated are too restricted. Until 

 such cells are tested under a great variety 

 of conditions, or better still, under all such 

 as are possible, their full capacity will not 

 be known. 



One of the more concrete matters of 

 disagreement over the cell theory concerns 

 the mode of connection between cells in the 

 organism. Are they completely separated 

 from each other by membranes or is their 

 internal substance or cytoplasm contin- 

 uous? Much importance hai5 been at- 

 tached to alleged protoplasmic bridges be- 

 tween cells and to the supposed syncytial 

 nature of the tissues. Adam Sedgwick 

 (1894) once described the vertebrate em- 

 bryo as an organism with nuclei lying in 

 a continuous reticulum, using this miscon- 

 ception to bolster up an erroneous theory 

 of the histogenesis of the nerve fiber. That 

 this question is not of such fundamental 

 importance as some would attribute to it is 

 shown by many considerations. 



While the eggs of insects and many other 



