THE PROPERTIES OF PROTOPLASM 7 



total disregard of our stimulus, a refractory period, 

 a period of complete insusceptibility ; or on the 

 other hand when we find an organism doing a thing 

 not in the least as the result of a stimulus, but 

 " spontaneously V or " automatically," when we 

 find the organism in possession of a power or ten- 

 dency to hold on the even tenor of its metabolic 

 way, to act in a particular manner when the external 

 conditions would constrain it to act in some 

 perfectly different manner, we cannot attribute 

 these things to affectability. Although as a term, 

 inertia of protoplasm, is metaphorical or at least 

 borrowed from the realm of physics, I intend it to be 

 used as a technical term for the physiological opposite 

 of affectability. Undoubtedly physiologists have 

 already recognised " physiological insusceptibility " 

 as a vital phenomenon; but, as a concept, "physio- 

 logical insusceptibility " is not coextensive with 

 functional inertia ; this insusceptibility is but one 

 mode of expression of the possession by protoplasm 

 of the fundamental property of functional inertia. 



How the term arose in my mind may be gathered 

 from what I * said at the meeting of the British 

 Medical Association at Ipswich in August 1900 : 

 " There are two kinds of inertia as properties of 

 matter (a) the inertia of matter at rest, and (b) the 

 inertia of matter in motion. That property of 

 matter in virtue of which it tends to maintain its 

 state of rest or of uniform motion in a straight line, 

 is called its inertia. The existence of inertia is the 



* D. F. Harris, Glasgow Medical Journal, April 1901, 



