24 AGE, GROWTH, AND DEATH 



the primary factor, because they can trace so many 

 alterations in the old which resemble diseased altera- 

 tions to the natural changes in the arteries by which 

 they acquire hardened and inelastic walls, which pre- 

 vent the proper response of the artery to the heart- 

 beat, upon which the normal healthy circulation 

 largely depends. 



Another interpretation, very curious and interest- 

 ing, is that which has been recently offered by the 

 same Professor Metchnikoff whom I have just men- 

 tioned. He has written a book upon the Nature 

 of Man, translated in 1903, and published in this 

 country. It is an interesting book. It gives a most 

 attractive picture, incidentally, of Metchnikoff him- 

 self, a man of pleasantly optimistic temperament, but 

 a man thoroughly imbued with the spirit which has 

 so often been attributed to contemporary scientific 

 men, of cold, intellectual regard towards everything, 

 towards life, towards man, towards mystery. For 

 him mysteries of all sorts have little interest. Those 

 things which are mysterious are beyond the sphere 

 of what can hold his attention. He must reside in 

 the clear atmosphere of definite, positive fact. This 

 mental bias is shown in his book. He reviews in a 

 happy way various past systems of philosophy ; he 

 describes various religions ; and he points out his 

 reasons for thinking that all of these are insufficient, 

 that there is no satisfaction to be derived from any 

 of the ancient philosophies or from any of the great 

 world religions. Nevertheless he is an optimist. He 



