THE PROBLEM 21 



of this phase of biological science, and endeavor to set 

 forth in an orderly and consistent maimer the present 

 state of knowledge of the subject. 



The problem of natural death has two aspects, one 

 general, the other special. These may be stated in 

 this way: 



1. Why do living things die? What is the meaning 

 of death in the general philosophy of biology? 



2. Why do living things die when they do? What 

 factors determine the duration of life in general and in 

 particular, and what is the relative influence of each of 

 these factors in producing the observed result? 



Both of these problems have been the subject of much 

 speculation and discussion. There has accumulated, 

 especially in recent years, a considerable amount of new 

 experimental and statistical data bearing upon them. I 

 hope to be able in what follows to show that this new 

 material, together with that which has for a long time 

 been a part of the common store of biological knowledge, 

 makes possible a clearer and more logically consistent 

 picture than we have had of the meaning of death and 

 the determination of longevity. Let us first examine in 

 brief review the broad generalizations about death which 

 have grown up in the course of the development of biology, 

 and which may now be regarded as agreed to by practi- 

 cally all biologists. 



BIOLOGICAL GENEEALIZATIONS ABOUT NATURAL DEATH 



The significant general facts which are known about 

 natural death are these: 



(A). There is an enormous variation in the duration 

 of life, both intra and inter-racially. Table I, which is 

 adapted from various authorities, is to be read with the 



