368 Death and Dissolution of the Organism 



pole in metamorphosis, the phenomenon is due to a 

 process of phagocytosis (and autolysis). We have 

 mentioned the fact that in the larva of the Amblystoma 

 the absorption of the gills and of the tail occurs simul- 

 taneously and that both must be caused by a constituent 

 of the blood. Such a constituent may be responsi- 

 ble for phagocytosis and autolysis in the organs under- 

 going absorption. Metchnikoff calls attention to the 

 fact that certain infectious diseases, e. g., syphilis, may 

 bring about precocious senility; and he mentions also 

 the senile appearance of young cretins which is due to 

 the diseased thyroid. "It is no mere analogy to sup- 

 pose that human senescence is the result of a slow but 

 chronic poisoning of the organism/' He assumes that 

 in man this poisoning is caused by the products of 

 fermentation in the large intestine and that the micro- 

 organisms responsible for these fermentations may 

 therefore be regarded as the real cause of senility in 

 man. Parrots which are long-lived birds have a limited 

 flora of microbes in their intestine, while cows and horses 

 which are short-lived in comparison with man possess 

 an extraordinary richness of the intestinal flora. But, 

 needless to say, it is not the quantity of microbes alone 

 which is to be considered, the nature of the microbes is 

 of much greater importance. 



Certain plants like the Californian Sequoia gigantea 

 may be considered as practically immortal since they 

 live several thousands of years; other plants, the an- 



