4 BIOTIC STRUCTURE AND BIOTIC ENERGY 



attempts to breathe and rapid hammering of the heart, there comes 

 sleep, lethargy, and death. 



Within physiological limits there is a delicate chemical equi- 

 poise of these fundamental processes of circulation and respiration. 

 And this is but an example of a general labile balance of colloids 

 favourable to chemical reaction which everywhere obtains in those 

 substances which constitute living matter. The oxygen balance 

 is only a particular case of that which holds also for nutrient 

 materials in general and for the thousand and one products of the 

 living cell's own activity or that of neighbouring cells. 



We may conveniently turn aside here to deal with a very general 

 aspect of the life of certain tissues which has excited in the past 

 endless work and wonder amongst physiologists namely, that it is 

 impossible to induce fatigue in those processes of nerve cells which 

 we call nerve fibres. 



It is obvious from what has been written above that fatigue 

 of a complete character, lasting even for two or three minutes in 

 the case of the cardiac muscle or of those nerve cells and processes 

 which govern the respiratory movements, would inevitably lead to 

 death. The chance of this is obviated by means of the colloidal 

 properties of those proteins which build up the cardiac muscle and 

 nerve cells. The structure of these substances is so arranged that 

 they possess a definite rhythm or reactivity of their own, which can 

 only be interfered with to a certain degree, but cannot be entirely 

 obliterated by outside interference or stimulation. After each 

 period of chemical activity in heart muscle or respiratory nerve cell 

 there is an interval called the " refractory period," during which 

 no amount of stimulation will cause a fresh discharge of energy in 

 the shape of a muscular contraction in the one case or a nervous 

 impulse down to the respiratory muscles in the other case. During 

 each period of rest there is a slow return to the initial condition in 

 labile balance of the colloids of the protoplasm. It is not until 

 this return or rearrangement is completed that another discharge 

 followed by another rearrangement can occur. 



The details of the chemistry of the discharge and subsequent 

 return to initial positions following it are at present unknown to 

 us, but we do know experimentally enough of the primary factors 

 involved to show that the above is a substantially correct represen- 

 tation of what occurs in each cycle. For example, the effects of 

 variations in osmotic pressure of carbon dioxide within the cell 



