THE PROPERTIES OF PROTOPLASM n 



is action, but it is limited action, action that cannot 

 be accelerated beyond certain limits, at a pace that 

 cannot be forced, at a degree of energy that cannot 

 be exceeded ; this is an expression of functional 

 inertia : through pure affectability as the only 

 property of cardiac protoplasm, such things could 

 not be. " The tissues set the pace," as the author 

 of the chapter on the Respiratory Exchange * 

 writes with regard to the inability of tissues to 

 perform respiratory exchanges at a greater rate 

 than a certain fixed one known as " the normal/' 

 and again, " rapid breathing does not bring about 

 a greater total exchange of gases than does slow 

 breathing." There is a tissue-pace which cannot 

 be voluntarily hurried. Again in the same work, 

 in the chapter on Purin Excretion f we are told that 

 the endogenous purin excretion is constant for each 

 individual, and does not depend on any known 

 physiological condition of the individual the 

 unknown here is functional inertia. We shall find 

 that inertia sets limits in connection with many other 

 phenomena, some of which will be subsequently 

 dealt with. These limits set to metabolic possi- 

 bilities are due to the possession of functional inertia 

 a property possessed contemporaneously with 

 affectability. Thus the manifestation of life at any 

 given instant is to be regarded as the resultant of 

 two co-existing but physiologically opposite functional 

 propensities or capabilities, the degree of whose 



* " Recent Advances in Physiology and Bio-chemistry." Edited 

 by L. Hill, p. 484. (London: Arnold, 1906.) t IMd* P- 4O3- 



