8 FUNCTIONAL INERTIA 



postulate in Newton's First Law of Motion 

 ' Every body continues in a state of rest or of 

 uniform motion in a straight line, except in so far 

 as it is compelled by forces to change that state.' 

 It is by reason of its inertia of rest that we find 

 it difficult to move the massive gate swung on 

 hinges of even relatively very small friction, there 

 is, in other words, ' lost time ' before the response 

 begins ; on the other hand, once we have set the 

 great gate swinging, it will move through a con- 

 siderable angle after we have ceased to push it ; this 

 is due to its inertia of motion or momentum." 



11 We have as biologists been so much impressed by 

 the universality of that property of living protoplasm 

 irritability or affectability, the power of responding 

 to a stimulus, that it is just possible we have under- 

 estimated a property no doubt of less importance 

 but still of interest which I venture to call ( functional 

 inertia.' ' I then proceeded to define it as that 

 " property of protoplasm whereby the living matter 

 contrives to remain in a functional status quo ante y 

 notwithstanding that it has received a stimulus, or, 

 having responded to the stimulus, it continues to ex- 

 hibit its functional activity for a certain time after the 

 stimulus as a form of energy has ceased to exist. 

 Living protoplasm furnishes us with examples of inertia 

 which might be called that of function." This was 

 written at the end of 1899 : since then I have become 

 so convinced of the truth of it that I would alter none of 

 it except the phrase in parenthesis <c no doubt of less 

 importance" to, (C no doubt of vast importance." 



