OLD AGE AND DEATH 361 



wear-and-tear theory of senescence, but many more detailed 

 suggestions have been brought forward. From a large 

 series of measurements, on the growth of guinea-pigs in 

 particular, Professor C. S. Minot of Harvard reached the 

 conclusion that the rate of increase in weight (measured 

 in percentage of total weight) steadily falls from the earliest 

 days after birth. Whereas the first ten per cent, of addition 

 in weight is made in about two days, the twenty-fifth 

 addition of ten per cent, (absolutely much greater) requires 

 nearly eighty-eight days. In fact, growth illustrates the 

 law of diminishing return. It is an uphill business all 

 the time, but the hill gets steeper and steeper as we go up, 

 until at length the gradient becomes impracticable and 

 growth stops. 



Minot compares the business of growing to the building 

 of a wall by one man : " The wall is built and grows larger, 

 develops, but the man grows more and more tired, and as he 

 grows more fatigued, and as the wall becomes higher, the 

 progress thereon becomes slower and slower, but the wall 

 has developed all the time. So we see that the body 

 develops all the time, but the power to continue the develop- 

 ment of the body steadily diminishes." Professor Minot 

 maintains that the law holds true of man, of chickens, of 

 rabbits, of dogs, of ferrets, and of some other animals. 



We cannot follow Professor Minot when he goes on to 

 say that there is from earliest youth onwards " a gradual 

 loss of vitality." We do not know no one knows what 

 vitality precisely means, but it surely means more than the 

 rate of growth in weight. It may be that in some domesti- 

 cated animals, such as sheep, cattle, and poultry, there is a 

 decrease in the range of vital activities and interests after 

 adolescence is past, and it may be that the two-year-old 

 child lives a more strenuous day than a man of sixty ; but 

 these are exceptional cases, When we consider how much 



