LIFE OF ELIE METCHNIKOFF 193 



death coincides usually with the ripening of the seed. 

 It has even been observed that it is possible to 

 retard the death of a plant by preventing it from 

 fructifying. For instance, lawns made up of grass 

 mown before it runs to seed remain green and living 

 whilst grass allowed to flower and bear seed becomes 

 yellow and dries up. It is a well-known fact that 

 fruits and seeds are frequently poisonous. Therefore 

 Metchnikoff supposed that the death of the plant may 

 be due to an auto-intoxication by poisons manu- 

 factured by it in order to defend its seeds and ensure 

 the next generation ; in Nature, the individual does 

 not count, but the species. Once the survival of this 

 is ensured the individual may disappear. 



A similar phenomenon of auto-intoxication is mani- 

 fested by lower vegetables, yeasts, and microbes. 

 Pasteur, who discovered the microbe of lactic fermen- 

 tation, found that this micro-organism, which itself 

 produces lactic acid, perishes because of the over- 

 production of this substance. Yeasts, again, cannot 

 bear an excess of alcohol, their own product. Thus 

 the vegetable kingdom offers us examples of the 

 absence of natural death as well as examples of a 

 natural death due to an auto-intoxication of the 

 organism. 



In the animal kingdom examples of natural death 

 are also to be found, but only very exceptionally. 

 Those examples are provided by Rotifera (inferior 

 worms) and by Ephemeridae. Their adult life is 

 reduced to the sexual act, almost immediately followed 

 by death without an external cause. Their life is so 

 short that they do not even feed and lack developed 

 buccal organs. That in itself constitutes an organic 

 cause of inevitable, i.e. natural, death. 



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