AUTHOR'S PREFACE 



IN preparing the material of a series of lectures, given 

 at the Lowell Institute in Boston in December 1920, for 

 book publication, I have deemed it on the whole best to 

 adhere rather closely to the original lecture mode of pre- 

 sentation with all its informality. Except for the fact 

 that the matter is here set forth in somewhat greater 

 detail than was possible under the rigid time limitations 

 of the Lowell Institute, and that the breaking into chap- 

 ters is slightly different, the whole is substantially as it 

 was presented in Boston. 



What I tried to do in these lectures was to bring 

 together under a unified viewpoint some of the more im- 

 portant contributions which have been made to our know- 

 ledge of natural death, from three widely scattered 

 sources: namely general biology, experimental biology, 

 and statistical and actuarial science. It will be obvious 

 to anyone who knows the literature from these fields 

 regarding natural death and the duration of life that in 

 such an amount of space as is here used, no one could 

 hope to cover a field so wide with anything approaching 

 completeness. To do so would require a series of volumes 

 in place of one small one. But this has in no wise been 

 my object ; I have instead hoped that the very incomplete- 

 ness itself of this work, necessitated by my limitations 

 of space and knowledge, might stimulate the reader to 

 penetrate for himself further into the literature of this 

 fascinating and important field of biology. To help him 

 to start upon this excursion a brief bibliography is 

 appended. It by no means completely covers the field, 

 but may perhaps serve as an introduction. 



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