122 INJURY, RECOVERY AND DEATH 



predictions are fairly accurate it is natural to infer that 

 the assumptions are in accordance with the facts. It is 

 evident from an examination of the figures that the equa- 

 tions enable us to predict with considerable accuracy the 

 behavior of tissues in solutions of NaCl and CaCl 2 , as well 

 as the recovery curves after any length of exposure to 

 either of these solutions. But we must not lose sight of 

 the fact that the predictive value of the equations does 

 not depend on the validity of these assumptions and would 

 in no way be impaired if they were to be given up. The 

 equations have a permanent value which is quite inde- 

 pendent of assumptions. 



The mechanism which has been postulated in devel- 

 oping these equations consists essentially of a series 

 of catenary reactions. There can be no doubt that, as 

 Loeb (1912, D) has emphasized, catenary reactions play 

 a large part in life phenomena, and it would seem that 

 the role assigned to them in the present discussion 

 involves no unreasonable assumption. 



A substance which acts as a member of such a caten- 

 ary system may, as Hopkins (1913) has remarked, be of 

 great importance in the organism even if present in very 

 small amount. 



It may be desirable to call attention to certain features 

 of this mechanism which are of general interest from 

 a theoretical viewpoint. It is evident that by means of a 

 simple catenary system we can account for practically all 

 the processes which occur in the organism. If such a 

 system is present in the egg we can easily picture all of 

 the subsequent development as due to this system, without 

 the introduction of any new reactions. All that we need 

 to postulate is that during development the relative rates 

 of the reactions change. The processes involved in irrita- 



