MAN. THE INSTINCT OF LIFE AND DEATH. 349 



known as sclerosis. It constitutes the charasteristic 

 lesion of a certain number of chronic diseases; and 

 these diseases are serious, for the stifling of the 

 characteristic elements by the less important ele- 

 ments of the conjunctive or packed tissue results in 

 the more or less complete reduction or suppression 

 of the function. 



The blood vessels also undergo this transformation, 

 and what we may call universal trouble and danger 

 ensue. This sclerosis of the arteries, this arterio- 

 sclerosis, not only deprives the walls of the blood 

 vessels of the suppleness and elasticity which are 

 necessary for the proper irrigation of the organs, but 

 it makes them more fragile. Thus it becomes a 

 cause of hemorrhage, which is a very serious matter 

 as far as the brain and lungs are concerned. 



It is remarkable that the alteration of the tissues 

 during old age should be exactly similar to this. 

 This is inferred from the few researches that have 

 been made on the subject — from those of Demange 

 in 1886, of Merkel in 1891, and finally from the 

 researches of Metchnikoff himself. It is a generalized 

 sclerosis. As its consequence we have the lowering 

 of the proper activity of the organs and the danger 

 of cerebral hemorrhage created by arterio-sclerosis. 

 The transformations of the tissues in old men are 

 therefore summed up in the atrophy of the important 

 and specific elements of the tissues, and their replace- 

 ment by the hypertrophied conjunctive tissue. This 

 sclerosis, is comparable to that of chronic diseases; 

 it is a pathological condition. Thus old age, as we 

 understand it, is a chronic disease and not a normal 

 phase of the vital cycle. 



On the other hand, if we ask ourselves what is the 



