Cell-Theory not Sufficient for Explaining Organism 183 



symbiosis has seemed to some biologists to furnish a type of 

 secondary association which is both sufficiently unitary and 

 sufficiently separatist, as regards the- ultimate elements, to be 

 available for the explanation of all biotic organization. 



The influence of this aggregative conception of the organ- 

 ism cannot be said to have been very great, so our examina- 

 tion of it need not be extensive. We will here consider 

 only the most plausible form of it, that namely which in- 

 vokes the principle of symbiosis. S. J. Holmes has worked 

 out a theory of this type more fully than any one else, so 

 far as I know; so his paper, entitled The Problem of Form 

 Regulation, will serve as the basis of our remarks. 



After speaking of the organism as a self-regulating 

 mechanism in which the whole is kept in functional equilib- 

 rium by the parts being "held in check" in some way, he 

 writes: "If we suppose that the various cells constituting 

 the body have each a different kind of metabolism, and that 

 the products of each cell are in some way utilized by the 

 neighboring cells, so that each derives an advantage from 

 the particular association in which it occurs, we may un- 

 derstand, in a measure, how this check may be brought 

 about. This supposed relation is realized in a simple scale 

 by the cases of symbiosis that occur between plants and 

 animals and between the algae and fungi of lichens. . . . 

 There is reason to believe that the same fundamental prin- 

 ciple which serves to explain the regulation of a simple 

 symbiotic community of animal and plant cells will apply 

 to highly developed organisms as well. We may regard the 

 body of a highly complex organism as a sort of symbiotic 

 ommunity." 4 



Although Holmes nowhere says explicitly that cells are 

 regarded as the vital units of his hypothetical organism, 

 vet most of his discussion clearly implies this. Thus, he 

 first considers the simple case of an organism consisting of 

 "two kinds of cells" ; then afterwards of one made of a 



