THE WONDERS OP LIFE 



old age or senility, by the gradual decay of the organs and 

 dwindling of their functions. The cause of this senility 

 and the ensuing natural death is determined for each 

 species of organisms by the specific nature of their 

 plasm. As Kassowitz has lately pointed out, the senility 

 of individuals consists in the inevitable increase in the 

 decay of protoplasm and the metaplastic parts of the 

 body which this produces. Each metaplasm in the body 

 favors the inactive break-up of protoplasm, and so also 

 the formation of new metaplasms. The death of the 

 cells follows, because the chemical energy of the plasm 

 gradually falls ofE from a certain height, the acme, of 

 life. The plasm loses more and more the power to 

 replace by regeneration the losses it sustains by the 

 vital functions. As, in the mental life, the receptivity of 

 the brain and the acuteness of the senses gradually 

 decay, so the muscles lose their energy, the bones 

 become fragile, the skin dry and withered, the elasticity 

 and endurance of the movements decrease. All these 

 normal processes of senile decay are caused by chemical 

 changes in the plasm, in which dissimilation gains con- 

 stantly on assimilation. In the end they inevitably lead 

 to normal death. 



While the gradual decay of the bodily forces and the 

 senile degeneration of the organs must necessarily cause 

 the death of the soundest organism in the end, the great 

 majority of men pass away through illness long before 

 this normal term of lifeis reached. The external causes 

 of this are the attacks of enemies and parasites, acci- 

 dents, and unfavorable conditions of life. These cause 

 changes in the tissues and their component cells, which 

 first occasion the partial death of particular sections, and 

 then the total death of the whole individual. The modi- 

 fications of the living matter which produce disease and 

 premature death are called necrobioses. They consist 

 partly of histolyses — that is to say, degeneration of the 



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