EVOLUTION OF COLLOIDS 143 



This observation is one of high import in 

 relationship to rhythmic processes, which 

 occur in many forms of living cells, such as 

 the nerve cells that guide respiration, and the 

 cells of contractile tissues like those of the 

 beating heart. 



The view was foreshadowed long ago by 

 Sidney Ringer that muscular contraction is an 

 incipient coagulation which becomes reversed 

 and again repeated in cyclic alternation. 

 This view was suggested by similarities in 

 chemical character between the products of 

 muscular contraction, and that coagulation 

 of the muscle juices which causes muscular 

 stiffening or rigor mortis after death. Heat 

 is not the only cause which can induce 

 incipient coagulation ; a slight change in 

 chemical reaction from alkaline towards acid 

 causes opalescence due to a running together 

 of the colloid into larger aggregates, which 

 commence to be big enough to interfere with 

 the light waves, and so cause opalescence. 

 If the amount of acid be increased the opales- 

 cence passes into true coagulation. Now a 

 living cell, such as a nerve-cell, may furnish 

 rhythmical stimulation to another, or itself 

 show rhythmical contractions, as in the case 

 of a muscle- cell, because it heaps up between 

 each contraction as a result of the chemical 



