FERTILIZATION IN PLANTS AND UNICELLULAR ORGANISMS 329 



subject. This conception was greeted with general approval, and 

 there are many people who still regard conjugation as a process by 

 which the capacity for life is renewed — a view which I must still 

 dispute as emphatically as -I did some years ago. 



In the first place, the observations on which this theory is based 

 admit of another interpretation, quite different from that which has 

 been assumed to be the only possible one. Maupas prevented con- 

 jugation, not perhaps because he had isolated individuals and their 

 progeny, but by exposing the whole colony of near relatives to 

 unusual conditions when conjugation was just about to set in, namely, 

 by supplying them with particularly abundant food. The need for 

 conjugation then disappeared, as, conversely, it could be called forth 

 at any time in a colony by hunger. But these are artificial conditions, 

 and indeed the breeding of Infusorians for months in a small quantity 

 of water on the object-glass certainly does not correspond to natural 

 conditions. We must admire the skill of the investigator who was 

 able to keep his colonies alive for months and years under such 

 artificial conditions, but we may venture to doubt whether the fate 

 of extinction which did ultimately overtake them was really due to 

 the absence of conjugation, and not to the unnaturalness of the 

 conditions. 



In any case a repetition and modification of Maupas' experiments 

 is very desirable, and would be of lasting value ^. 



Let us, however, assume for the moment not only that Maupas' 

 observations were correct, which I do not doubt, but also that they 

 were rightly interpreted. Would they in that case afibrd a proof 

 that amphimixis means a rejuvenescence of the jxjwer of life ? To my 

 thinking, not in the remotest degree. 



It certainly seems as if this were true at the first glance ; the 

 colony which is prevented from conjugating goes on multiplying for 

 a considerable time, often indeed for hundreds of generations, but this 

 may be compared with sufferers from hunger, whose life does not 

 cease at once if the feeling of hunger is not appeased. 



1 Since the above was written Calkins has made a series of new experiments, the 

 results of which differed in several respects from those yielded by Maupas' experiments. 

 When his infusorian-cultures began to grow weaker, as happened frequently and at 

 irregular intervals, he was always able to restore them to more vigorous life by a change 

 of diet, and especially by substituting grated meat, liver, and the like for infusions of 

 hay. Certain salts, too, had the same effect : the animals became perfectly vigorous 

 again. Calkins believes that chemical agents, and especially salts, must be supplied to 

 the protoplasm from time to time. He reared 620 generations of Paramrjecium 

 v,-ithout conjugation. But the 620th was weakly and without energy. The addition 

 of an extract of sheep's brains made them perfectly fresh and vigorous again. Further 

 experiments in this direction are to be desired, but, according to those of Calkins, it is 

 probable that Infusorians can continue to live for an unlimited time even without 

 conjugation. 



