THE BIOLOGY OF THE CELL SURFACE 



depend upon each other. Apparently, connective tissue 

 exercises merely a passive restraint upon the subjoined 

 tissues; it isolates and insulates. It is otherwise with the 

 interdigitated cells in a given tissue. Their interdigita- 

 tions constitute a means for bringing the cells directly into 

 connection. 



On the side of theoretical biology intercellular prolonga- 

 tions deserve our interest. Hammar suggested that by 

 them the unity of the multicellular organism may be main- 

 tained, seeing in them a basis for some support of Whitman's 

 idea of the inadequacy of the cell theory for development, 

 on which I have commented above; here I wish to point 

 out the following: 



A multicellular organism, as a human being, is a unit 

 and acts as such through integration. The cellular con- 

 nections of the first grade in importance are those of nerve. 

 To secure unified action of the organism is a function of the 

 nerve cells primarily. Alongside with nerve integration, 

 we place that by the hormones; for they come from glands 

 upon which life depends, without which the organism dies; 

 these, except the pancreas, are derivatives of or include 

 derivatives of the nerve tissue or that from which the nerve 

 tissue is derived, namely, the ectoderm; these glands are 

 the pituitary body, the thyroid apparatus and the adrenal 

 body.^ 



This nerve integration, as that of the three important 

 hormones named above, is remarkable because of the fact of 

 the ectodermal origin of its carriers. As we shall see in 

 a later chapter, ectoderm cells arise from those cells in 

 the developing egg which are richest in ectoplasm. Hence 

 the highest form of integration in the complex multicellular 



^ The internal secretion of the pancreas is derived from cells which 

 are neither nervous nor ectodermal in origin and therefore the pan- 

 creas cells arc an exception here. 



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