22 AGE, GROWTH, AND DEATH 



the elastic cartilaginous rib becomes bony, nothing 

 different is happening from that which happened be- 

 fore, 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 carti- 

 lage was changed gradually into bone, thus producing 

 the characteristic, normal, efficient 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 favourable, but 

 unfavourable. 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 pre-em- 

 inently 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 Pasteur 

 Institute in Paris, some of whose publications many 

 of you have doubtless read, that his conception of 



