December 13, 1912] 



SCIENCE 



805 



mal material, including some epidermis 

 together with deeper tissue, is isolated 

 under proper conditions, the fragment may 

 become more or less completely covered 

 over by extension of the epidermis. This 

 covering of outside surface by epidermis 

 of uniform thickness and character is dis- 

 tinctly a tissue phenomenon due to a cer- 

 tain organization inherent in the tissue. 

 It is not dependent, at least not necessarily 

 dependent, upon the organization of the 

 animal as a whole. A distinction between 

 tissues and organs can not always be 

 sharply made. However, it is clear that 

 the action of an organ is not necessarily 

 dependent upon the integrity of the animal 

 to which it belongs. A vertebrate heart, 

 under proper conditions of temperature 

 and fluids, will continue its rhythmic ac- 

 tion long after removal from the animal. 

 (So, indeed, will an excised strip of its 

 muscular wall.) An excised kidney long 

 retains the capacity for functional activity. 

 Under normal circumstances it is depend- 

 ent for its oxygen and nutrition upon the 

 animal to which it belongs. But in its 

 organization as a kidney, it seems to be 

 quite independent of the animal as a whole. 

 And finally, there are activities which are 

 distinctly functions of the animal as a 

 whole — the hydra seizing and swallowing 

 a Cyclops, a dog following a scent, a cat 

 fighting, a kitten playing. Here we see 

 the animal acting as a unit. Its action is 

 relatively simple and intelligible just as its 

 external form is. But analysis of the ac- 

 tion resolves it into a complex of physiolog- 

 ical units corresponding to a complex of 

 structures involving perhaps aU of the sub- 

 ordinate organizations of the animal. 



Comparing the units of these several 

 grades of organization, the cell stands 

 forth with peculiar prominence. It has 

 always appeared so to the biological mind. 



The fact that every animal part, upon 

 analysis, reduces to cells, the uniformity 

 in size and visible structure of these 

 bodies, make tTiem conspicuous as uni- 

 versal morphological units. The tissue, 

 and even the organ, is ordinarily much less 

 definitely formed and limited, less sharply 

 individualized. The organ-system is obvi- 

 ously a somewhat arbitrarily distinguished 

 unit. In strict morphological sense, at the 

 first step of analysis the whole individual 

 resolves itself directly into organs. The 

 natural tendency, then, is to regard the cell 

 as the essential morphological and physio- 

 logical unit. In fact, so important does 

 the cell appear that we have been inclined 

 to consider the relation between cell and 

 organ, or even between the cell and the 

 whole individual, to be a direct one rather 

 than one which is indirect by way of such 

 intermediate systems as may exist. 



In presenting this familiar sketch of the 

 plan of an organism, I use the word, organ- 

 ization, in its ordinary sense. It is not 

 structure nor is it function. It consists in 

 certain definite and obvious relations of 

 functions, and therefore of structures too. 

 It asserts nothing as to the nature of these 

 relations and it implies nothing as to how 

 they have come to exist. Just here we 

 meet some serious biological problems. 

 What is the nature of those relations which 

 constitute organization? How do they 

 come into being? By what and how is it 

 determined that a group of cells shall be 

 associated together to constitute an epi- 

 thelium of definite and constant thickness 

 and character? In muscle tissue how does 

 it come about that thousands of cells are 

 substantially alike and capable of opera- 

 ting harmoniously together in response to 

 an effect received from nerves? What is 

 it that affects a mass of tissue of a certain 

 kind in such a way that it assumes the 



