BIOTIC STRUCTURE AND BIOTIC ENERGY 5 



above described show that this substance is one of the important 

 factors in the above discharge and rearrangement, the speed of 

 which varies with the carbon- dioxide pressure. But whether the 

 carbon dioxide accumulates in combination with the proteins 

 during the discharge, and then has to be disentangled and given 

 off during the pause, or, conversely, whether carbon dioxide 

 accumulates, attaching itself to the colloidal proteins during the 

 pause, and then is suddenly and explosively thrown off during the 

 discharge, is somewhat difficult to determine. The fact, however, 

 that slightly increased pressure of carbon dioxide hastens the 

 rhythm of explosion and recovery, while diminished pressure slows 

 the rhythm, would seem to indicate that irritation is heaped up to 

 discharging point as carbon dioxide accumulates in union with 

 protein, and that at the explosion carbon dioxide is set free. 



Again, the presence in sufficient concentration of certain 

 inorganic ions, such as those of potassium, calcium and phosphates, 

 is absolutely essential to the regular discharge of the cardiac cycle, 

 with due alternations of the two phases of rest and activity. 



It can be shown experimentally, by varying the osmotic pressure 

 of each of the above ions in the circulating fluid supplied to an iso- 

 lated and perfused heart, that characteristic variations occur in 

 each case in the rate and force of the heart-beat, and in the form of 

 the time relations of contraction and relaxation as shown by the 

 shape of the curve of the heart-beat. 



These effects were first worked out experimentally by Sidney 

 Ringer, and have now been shown to be of widespread application 

 for all types of cells possessing, as nearly all cells do, the tendency 

 towards a rhythmic discharge. 



A mechanical analogy may illustrate the vibrating equilibrium 

 of these poised chemical factors in the living cell. Let us consider 

 the mechanical system composed of the mainspring of a watch and 

 its train of wheels leading to the oscillating balance wheel and its 

 hair- spring, and compare this with the beating of the mammalian 

 heart. The balance wheel with its tiny hair-spring may represent 

 the cardiac muscle, and the mechanical pressure giving energy from 

 the mainspring represents the nutritive supply of chemical energy 

 sent in for the heart-beat by the blood plasma and oxygen. Now 

 the rate of vibration in the watch is regulated by the weight or 

 inertia of the balance wheel and the reaction of the hair- spring. 

 Two similar factors regulate the heart-beat viz., the nature of the 



