GROWTH AND SENESCENCE. 905 



reous, the crystalline lens gradually loses its elasticity, the muscles 

 lose their vigor, the hairs their pigment, the nuclei of the nerve 

 cells become smaller, and so on. In every- way there is increasing 

 evidence, as the years grow, that the metabolism of the living mat- 

 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. We do not understand the nature of these limitations, that 

 is, the ultimate causes of senescence. Many examples of unusual 

 longevity are on record, the most authentic being probably that of 

 Thomas Parr. An account of his life and the results of a postmor- 

 tem examination by Harvey are given in volume iii of the " Philo- 

 sophical Transactions of the Royal Society of London." "He died 

 after he had outlived 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- 

 dividual dies, we must believe that the protoplasm of the repro- 

 ductive elements is not subject to natural death, but has a self- 

 perpetuating metabolism which under proper conditions makes it 

 immortal. Weissmann f designates the protoplasm of the germ cells 

 as germ-plasm, that of the rest of the body as somatoplasm, and 

 inasmuch as the former continues to propagate itself indefinitely 

 under proper conditions, while the latter has a limited existence, he 

 concludes that originally protoplasm possessed the property of 

 potential immortality. That is, barring accidents, disease, etc., it 

 was capable of reproducing itself indefinitely. He assumes, more- 

 over, that this property is exhibited at present in many of the sim- 



* A picture of Parr painted by van Dyck (1635) is exhibited in the Royal 

 Gallery, Dresden, No. 1032. 



t Weissmann, "Essays upon Heredity and Kindred Biological Prob- 

 lems"; also ''Germ-plasm" in the "Contemporary Science Series.' 1 



