AGE, GBO]YTH AXD DEATH 489 



life in our demands upon our organism, and still find that our body, 

 is capable of making the necessary response. Ordinarily the amount 

 of blood which we require is moderate in amount — moderate in the 

 sense that the destruction of the blood continually going on in the 

 body is not a very rapid process ; but if, through some accident, a person 

 loses a large quantity of blood then by one of these teleological reac- 

 tions of which I have spoken, the production of new blood is increased, 

 the loss is soon made up, and we discover that the blood, so to speak, 

 has been repaired. Or when a little of the skin is lost, it quickly heals 

 over. That again is due to the power of repair. Ordinarily so long 

 as the skin remains whole that power is not called into action, but 

 if a wound comes, then the regenerative force resident always in the 

 skin, but inactive, comes into play and produces the mending which 

 is such a comfort. So in old people, some of this luxury of reparative 

 power persists, so that they can recover from wounds in a far better 

 way than we should imagine if we judged them only by the general 

 physiological and anatomical decline exhibited throughout all parts 

 of the body. Some of the luxury of repair comes in usefully in old age. 

 Xow if we consider all these changes in the most general manner, 

 we perceive that they are clearly of one general character; they imply 

 an alteration in the anatomical condition of the parts; but it is an al- 

 teration which does not differ fundamentally in kind from the alterations 

 which have gone on before, but it does differ in the extent and in part 

 in the degree to which these alterations have taken place. When the 

 elastic cartilaginous rib becomes bony, nothing different is happening 

 from that which happened before, for there was a stage of development 

 when the entire rib consisted of cartilage, and in the progress of 

 development toward the adult condition that cartilage was changed 

 gradually into bone, thus producing the characteristic, normal, effi- 

 cient bony rib of the adult. When old age intervenes, the change of 

 the cartilage into bone goes yet further, but it progresses in such a way 

 that it is no longer favorable, but unfavorable. We have then in this 

 case a clear illustration of a principle of change in the very old which 

 is, I take it, perhaps sufficiently well expressed by saying that the 

 change which is natural in the younger stage is in the old carried to 

 excess. But there is in addition to this, something more, of which 

 I have already spoken, namely the atrophy of parts, and by atrophy 

 we mean the diminution, the lessening of the volume of the part. 

 There is a partial atrophy of the brain in consequence of which that 

 organ becomes smaller; there is an extensive atrophy of the muscles 

 in consequence of which their volume is diminished, and their efficiency 

 decreased. Atrophy is preeminently characteristic of the very old, 

 and we see in very old persons that it becomes each year more and 

 more pronounced. Indeed, it has been said recently by Professor 

 Metchnikoff, a distinguished Russian zoologist, now connected with the 



