142 THE LAW OF BIRTHS AND DEATHS 



requires no great stretch of imagination to infer that the 

 sperm cell and ovum are governed by the same biological 

 laws as the organisms from which they were originally 

 derived. Although we are not expressly so informed, 

 yet it seems fairly obvious that if starvation were carried 

 beyond a certain stage conjugation would become im- 

 possible, since the organisms would enter into a dying 

 condition. It might have been expected that the exhaus- 

 tion resulting from repeated asexual divisions would 

 have ultimately overcome the effects of high feeding, 

 and have rendered conjugation possible. But possibly 

 the term " senile decay " is justified and the effects of 

 too prolonged asexual reproduction analogous with the 

 effects of old age in the higher organisms rather than 

 with the effects of fatigue or under-feeding. 



The experiments of Maupas were not quite complete. 

 Subsequent observations have shown that asexual division 

 can continue indefinitely among these lowly organisms 

 if the culture mediums in which they live are kept quite 

 pure or constantly changed. This has been demonstrated 

 by several experimenters, and L. L. Woodruff has carried 

 cultures of Paramsecium through two thousand genera- 

 tions, extending over three and a half years. Woodruff 

 concludes that these organisms excrete products which 

 are poisonous to themselves, and that so long as the 

 infusions in which the organisms live are kept perfectly 

 free from these excretions, there is no reason why they 

 should not continue to divide indefinitely. But a small 

 addition of the products of excretion renders conjugation 

 necessary, or produces the symptoms of " senile decay." 

 If senile decay among the higher animals be looked upon 

 as due to the imperfect elimination of waste products, 

 there may be some analogy between the two cases. But 

 the net result of these experiments is that so long as the 

 conditions are such as to keep the organisms in full health 



