1014 THE PHYSIOLOGY OF REPRODUCTION. 



ter of the body becomes less and less perfect; the power of the 

 protoplasm itself becomes more and more limited, and we may 

 suppose would eventually fail, bringing about what might be called 

 a natural death. As a matter of fact, death of the organism usually 

 results from the failure of some one of its many complex mechanisms, 

 while the majority of the tissues are still able to maintain their exis- 

 tence if supplied with proper conditions of nourishment. The phys- 

 iological evidences of an increasing senescence warrant the view, 

 however, that death is a necessary result of the properties of living 

 matter in all the tissues except possibly the reproductive elements. 

 The course of metabolism is such that it is self-limited, and even 

 if perfect conditions were supplied natural death would eventually 

 result. As a rule, however, death is, so to speak, accidental 

 rather than natural. This point of view was emphasized by Ray 

 Lankester in the distinction which he drew between specific 

 longevity and potential longevity. By specific longevity he des- 

 ignated the expectation of life at birth of a normal individual, 

 this expectation being determined by the interaction of two fac- 

 tors — namely, the innate constitutional properties of the proto- 

 plasm and adverse environmental conditions. By potential lon- 

 gevity is meant the duration of life which might be expected 

 under an ideal environment. The average specific longevity, 

 reckoned from birth, is greatest in the most civilized communities 

 and reaches at present the length of forty-five to fifty years. 

 Quite probably the advances of medical knowledge, especially of 

 preventive medicine, may continue to increase the average of this 

 expectation of life. What the potential longevity of man would 

 be if protected from all accidents and disease cannot be stated 

 with any certainty, but on the basis of the exceptional cases of 

 longevity reported we may assume that it would exceed one 

 hundred years. The most authentic of the cases reported of 

 unusual longevity is that of Thomas Parr. An account of his 

 life and the results of a postmortem examination by Harvey 

 are given in Volume III of the "Philosophical Transactions of 

 the Royal Society of London." "He died after he had out- 

 lived nine princes, in the tenth year of the tenth of them, at 

 the age of one hundred and fifty-two years and nine months." 

 The immediate cause of his death was attributed to a change 

 of food and air and habits of life, as he was brought from Shrop- 

 shire to London, "where he fed high and drunk plentifully of the best 

 wines."* With reference to the phenomenon of senescense as a neces- 

 sary attribute of living matter, Weissmann has called attention to the 

 fact that inasmuch as the species continues to exist after the in- 



* A picture of Parr painted by van Dyck (16.35) is exhibited in the Royal 

 Gallery, Dresden, No. 1032. 



