The Intimate Causes of Old Age. 221 



seated in unicellular life. Sexual conjugation gave best 

 results when the cells were of "stranger" parentage. If 

 sexual conjugation were too long deferred, till the succes- 

 sive generations had grown very much enfeebled and 

 senescent, it was either unsuccessful or failed to be under- 

 taken. Under natural conditions it took place when the 

 individual generations were at their best. 



Why individual generations from the same parent fail 

 to conjugate with entire success, is thus far as little 

 understood in unicells as in animals. The proper ele- 

 ments for the sexual reaction appear to be lacking, as if 

 there were too great a sameness, too much identity or 

 similarity in the sexual elements of the paranucleus and 

 pronucleus. To obtain the needful sexual reaction or 

 stimulus between the cells, they should come from 

 another stock and have been nourished in another place, 

 in a different environment. 



Where sexual conjugation did not take place the 

 generations from the same cell parent, as time went on, 

 became smaller and often deformed. After several hun- 

 dred generations the descendants of a single cell parent 

 all die and the line becomes extinct. 



In principle nothing different takes place in multicellu- 

 lar life in animals and man. There are modifications of 

 the same method, due to the extensive organization of the 

 cells, but no departure from the principle of cell renewal 

 by an interblend of the nuclear substance of two cells. 



