200 C. M. CHILD 



different conditions of nutrition, different degrees of regulation, 

 etc. 



It is of course possible that further use of the method may 

 bring to light further complicating or limiting factors but it is 

 certain that the method is capable of very wide application. But 

 in addition to the immediate results the method gives us a means 

 of attack on various problems which have not heretofore been 

 open to investigation. 



During the last few years I have used both the direct and the 

 indirect methods in a very large number of experiments and with 

 a variety of forms. The results obtained afford a new insight 

 into the dynamics of living organisms, they throw light on the 

 problem of physiological polarity and symmetry, they afford a 

 dynamic basis for the law of antero-posterior development and 

 thej^ have demonstrated that changes in the rate of metabolic 

 reaction may bring about changes in the number, localization, 

 degree of differentiation, etc., of definite morphological characters. 

 Besides this they have made it possible to demonstrate the essen- 

 tial similarity between the process of regulation by which a piece 

 gives rise to a whole and the other forms of reproduction and 

 development in nature. They have given us a new viewpoint 

 from which to consider the questions of senescence and rejuvenes- 

 cence. And finally, certain of the results obtained have a very 

 direct bearing upon the problem of inheritance. Some of the 

 more important results have already been briefly presented 

 (Child '12 b) and these and others will be more fully considered 

 in following papers. 



IV. THE ACTION OF DEPRESSING AGENTS IN GENERAL 



1 . The nature of the action of depressing agents on Planaria 



It is not my intention to discuss at length the problem of nar- 

 cosis, but merely to call attention to certain points. 



The poisonous effect of the cyanides is very generally regarded 

 as due, at least in large part, to a retardation or inhibition of 

 some sort of the oxidation processes. According to Geppert 

 ('89) they render the tissues incapable of uniting with oxygen. 



