viz THE STAGES OF LIFE AND DEATH 293 



protoplasm, which undergoes slow and continuous change during 

 life, in the sense that the functions of restoration, repair, and 

 compensation gradually become less perfect and less complete, 

 until finally all vital activity ceases. 



We may say positively that the cataplastic phase of life is 

 absolutely physiological ; it corresponds with the natural decline 

 of every living being, which inevitably ends in death, the 

 completion of the cycle. 



Senile involution may be aggravated and hastened by many 

 other causes of decay to which our flesh is heir ; in such cases, 

 however, senility is a morbid condition, not a function of age, 

 and may be noted before the close of maturity and belongs to the 

 department of pathology. Old age begins at fifty in women and 

 at sixty in men. Some scientists subdivide it into three stages : 

 that from sixty to seventy years of age, when the first signs of 

 decay appear (viridis senectus) ; seventy to eighty, the phase of 

 frailty (grandaevi aetas); and the period from eighty to the 

 close of life, the phase of longevity, or aetas decrepita. These 

 divisions are artificial, not being distinguished from one another 

 by anatomical or functional characteristics : their appearance 

 and expiration may be hastened or retarded by various external 

 and internal conditions, such as climate, special kinds of work 

 and nourishment, race, sex and hereditary tendencies. 



The problem of human senility and of its ultimate consequence, 

 death, has given food for thought to many, from the theologians 

 and philosophers of ancient times to the most modern of biologists. 

 They have all regarded it as the most interesting and important 

 of life's problems. It will therefore be well to take a rapid survey 

 of the views which have succeeded one another on the subject of 

 old age and death, since these views afford us an idea of the general 

 advance in scientific knowledge. 



Greek philosophy regarded the process of senility as intimately 

 connected with the gradual development of innate heat, by which 

 they understood and symbolised the sum total of the virtual 

 energies and hereditary tendencies accumulated in the germ. 

 After the discovery of the circulation of the blood and lymph, 

 the condition of the heart and blood-vessels came to be regarded 

 as an essential factor in determining the different ages of life, 

 old age and death included. After the earliest microscopical 

 researches the state of the fibre, the gradual changes of the con- 

 stitution of the organised elements of the tissues, were considered 

 important for the determination of the ascending and descending 

 phases of life. Finally, with the development of bacteriology and 

 the chemistry of the secretions, the bacteria found in the intestines 

 and the influence of the glands of internal secretion were considered 

 the fundamental conditions of growing old. 



Aristotle, in his works De juventate et senectute and De 



