THE REFRACTORY PERIOD AND FATIGUE 167 



that the duration of the refractory period is influenced in like 

 manner by temperature. Indeed, Kronecker^ found some time ago 

 that in the isolated frog's heart a much more frequent rhythm of 

 stimulation is effective at a higher than at a lower temperature. 

 When the heart is stimulated at a temperature of 11-12° C. with 

 twelve rhjrthmical induction shocks in the second, every stimulus 

 is operative and produces a systole. If a stimulus of the same 

 frequency is used at a temperature of 5° C, the heart responds 

 merely to every second stimulus. This shows that the refractory 

 period is of longer duration at a lower than at a higher tempera- 

 ture. 



A factor of particular interest is the supply of oxygen, for we 

 know its fundamental importance in all aerobic organisms in the 

 breaking down of the living substance. The life of these organ- 

 isms is primarily dependent upon the supply of oxygen from 

 without. Organic reserve substances for restitution after dis- 

 integration are contained in ample quantity in the reserve stores in 

 the living cell substance, whereas oxygen is present in very small 

 quantities in relation to the former. It is, therefore, self-evident 

 that the rapidity of the breaking down processes is very closely 

 dependent upon the amount of available oxygen at hand. Never- 

 theless it is not the absolute quantity but the relative amount of 

 oxygen in relation to the momentary requirement which is of 

 importance. For instance, the quantity of oxygen present may 

 completely suffice for the oxydative disintegration in the metab- 

 olism of rest or at lower temperature, whereas the same amount 

 would be much too small to meet the demand increased by exci- 

 tation or at higher temperature. In the latter case "a relative 

 deficiency of oxygen" occurs. I have introduced the term "rela- 

 tive deficiency of oxygen"^ for I have found that a number 

 of authors by neglecting the relations of the available oxygen 

 to that which is required at the moment have been led to false 

 conclusions. There is no living object so preeminently fitted 

 to demonstrate in such a striking manner the dependence of 



1 H, Kronecker: "Das charakteristische Merkmal der Herzmuskelbewegung.'' 

 Beitrage zur Anatomie und Physiologic als Festgabe Carl Ludwig ztim 15 October 

 1874 gewidmet. Leipzig 1874. 



2 Max Verworn: "Allgemeine Physiologie." V. Auflage. Jena 1909. 



