598 Mr. Charles Merrier [May 3, 



circumstances. It has taken a set. It has acquired a statical memory 

 of the experience that it has undergone. 



But now if we watch the stick, we shall find that this is not the 

 end of the process. It has taken a set, it is true, but the set is not 

 permanent. After remaining at rest for a certain time, the set begins 

 to diminish, at first slowly, then more rapidly, and then with a speed 

 that gradually diminishes. If we clamp the stick in a vice, and 

 observe it carefully, we sball find that it continues for hours, and 

 even for days, to return with diminishing speed towards its original 

 shape. This is a new phenomenon, to which unorganised bodies 

 exhibit no parallel. The stick takes a set, but the set is not per- 

 manent. It is a temporary set. It disappears, or at least it 

 diminishes. The return towards its original shape is made, not with 

 a single bound and there an end, but with an initial bound, and then, 

 after a pause, by further progress, for a short time with increasing, 

 and thereafter for a long time with diminishing, velocity. The 

 statical memory of the unorganised body, once acquired, undergoes 

 no change. That of the organised body does not remain constant, 

 but soon begins to fade, and fades at first with increasing, and 

 subsequently with diminishing, speed. 



Still more different from that of the unorganised body is the 

 dynamical memory of the organised tissue. When once a bar of iron 

 has been bent, the application of the same force will produce no 

 further distortion, however often it may be repeated, or however long 

 it may be applied. The production of a set makes more difficult the 

 production of a further set in the same direction. But when a stick 

 has once been bent sufficiently to produce a temporary set, then the 

 application of the same force will produce a further set. Its repeated 

 application will increase the set in some proportion to the frequency 

 of the repetition ; its continued application will increase the set in 

 some proportion to the time of its continuance. Thus the dynamic 

 memory of the organised body is opposite to that of the unorganised 

 body. 



Such are the differences in the behaviour of the two substances 

 when distorted beyond their respective elastic limits. But there are 

 differences also when the distortion is within these limits. When a 

 pieco of steel suffers a distortion which is well within the limit of its 

 elasticity, it will retain its former shape however often it may suffer 

 distortion. The hair-spring of a watch will suffer distortion of its 

 shape ten million times in the course of a year, and yet after many 

 years of incessant action it will exhibit no perceptible change of 

 shape. With organised bodies the results of repeated application of 

 force are different. A bow that is in constant use " follows the 

 string " at last ; that is to say. it becomes permanently bent. It 

 attains a true permanent set, which undergoes no diminution. So 

 too. the top joint of a fishing-rod becomes permanently curved. A 

 shelf will sag under a weight, and if the weight is at once removed, 

 will entirely recover itself ; but apply the weight sufficiently often, 



