Decembee 13, 1912] 



SCIENCE 



807 



physiological economy of the whole animal, 

 we need only consider that, had it been 

 otherwise, the "struggle for existence" 

 must have long since made an end of the 

 matter. 



An alternative view attributes the har- 

 monious operation of a system to the action 

 of some dynamic agent or energetic com- 

 plex which exercises general control over 

 the members of the system. These mem- 

 bers must be similarly constituted in order 

 that they may properly respond to the con- 

 trolling agent. The control may be con- 

 ceived to consist in the action of a superior 

 dynamic agent upon an inferior system, or 

 in some effect of the system as a whole 

 upon its individual members. 



It is quite obvious that the activity of 

 one organ does affect the tissues and cells 

 of other organs and that the units of one 

 system are dependent in a variety of ways 

 upon other systems. An epidermal cell is 

 dependent upon the digestive, respiratory, 

 circulatory and excretory systems, and less 

 directly upon the nervous and other sys- 

 tems. There are numerous other relations, 

 perhaps equally important even if less ob- 

 vious, such as exist between the ductless 

 glands and other organs and tissues in 

 vertebrates. Indeed, it appears likely that 

 we are at present very far from a complete 

 knowledge of the extent to which internal 

 secretions or hormones may serve in the 

 correlations of organs. In ontogeny hor- 

 mone action may play a role of utmost 

 importance as a "mechanism for organic 

 correlation."^ The nervous control of 

 muscular, secretory and other activities 

 affords what is, in a sense, the most con- 

 spicuous instance of control exerted by one 

 part over another part. But while such 

 relations as those involved in nervous con- 



^ Parker, G. H., 1909, "A Mechanism foi Or- 

 ganic Correlation," American Naturalist, Vol. 43, 

 April, pp. 212-218. 



trol and hormone action may be absolutely 

 essential to the normal operation of the 

 various organs and systems of the animal, 

 it by no means necessarily follows that 

 such relations involve any general control 

 of the organization of the elements of one 

 organ by the action of another organ. So 

 far as the nervous system is concerned, 

 quite the reverse may be true. An agent 

 which controls certain activities of a group 

 of elements may in no way be responsible 

 for the fact that those elements are capable 

 of responding to its control. The relation 

 of the nervous tissue to the muscle tissue 

 may he exceedingly limited in that it is 

 perhaps only the processes concerned with 

 contracting that are under nervous control. 

 The general organization of the muscle is 

 not, so far as we know, due to nervous 

 control. Professor E. G. Harrison and his 

 co-workers have achieved results of far- 

 reaching importance in demonstrating that 

 the ontogenetic differentiation of muscle 

 tissue is independent of any action of the 

 nervous system. In the fully differenti- 

 ated muscle tissue exists an organization 

 which renders the tissue capable at any 

 instant of proper response to nervous stim- 

 ulation. What is it that maintains this 

 organization in the muscle ? An answer to 

 the question may be offered by asserting 

 that the histological peculiarities of muscle 

 tissue are due to germinal preformation, 

 and having been so determined and devel- 

 oped, they persist. This may or may not 

 be satisfying. Tissue cells are not struc- 

 tures like stone blocks laboriously carved 

 and immovably cemented in place. They 

 are rather like local eddies in an ever- 

 flowing and ever-changing stream of fluids. 

 Substance which was at one moment a 

 part of the cell passes out and new sub- 

 stance enters. What is it that prevents 

 the local whirl in this unstable stream from 



