136 PROTOPLASMIC AGE OF PROTOZOA 



these "noble" cells atrophy, their positions being taken by the con- 

 nective-tissue cells. 



Here, then, is the condition of old age; the somatic cells lose what 

 germinal power they possess through physiological usury; their 

 potential of physiological activity is greatly reduced; the function of 

 the organ is impaired and the entire organization correspondingly 

 weakened; the useless cells are attacked by phagocytes (?) (Metch- 

 nikoff), and they are replaced by the non-functional connective tissue. 



Old age, therefore, is a biological condition of protoplasm, char- 

 acteristic alike of the lowest protozoon and the highest mammal. 

 Its progress is inexorable, its advent inevitable, while the only per- 

 manent plasm is that which has the highest power of germinal activity, 

 and this is contained in the germ cells. Here, however, that other 

 unfathomable mystery of life — fertilization, or its equivalent — is 

 essential for the proper stimulation of the latent developmental activity 

 and the distribution of the somatic and germinal cells in a new indi- 

 vidual organism. How this occurs in paramecium and other protozoa 

 will be shown in the following chapter. 



While the experiments on the lowest animals show that old age is a 

 necessary condition of vitality and inherent in all protoplasm, it does 

 not follow that man or any other animal has made the best possible 

 use of the vital endowments. It may very well be, as Metchnikoff 

 maintains, that the traditional three score and ten is not an adequate 

 allowance for man, and it is conceivable that the normal length of life 

 may be increased by careful living to four or five score of years or 

 more. If there is a certain amount of vitality upon which one can 

 draw, it is obvious that the faster it is drawn the shorter will it last, 

 and conversely, the more saving one is by careful living, the longer will 

 it endure. Only one thing are we sure of, and this is that somatic 

 vitality, whether in protozoon or man, is a peau de chagrin which con- 

 stantly diminishes with use until finally nought is left. 



