VITALITY 259 



they have become adapted to the artificial conditions of cultivation 

 and continue to live and divide so long as these conditions are 

 maintained but they must divide. 



The question of "normal" or "abnormal" environment after all 

 appears to me to be of an academic nature, and I cannot agree with 

 Woodruff and his followers in their belief that natural death is 

 not inherent in ciliates under natural, or, as he calls it, "normal" 

 conditions. Nor can I accept his further conclusion that the life 

 cycle of a ciliate is a "myth." It is quite evident that the cycle 

 may be greatly varied by reason of external conditions and it is 

 plainly obvious that it has no definite or fixed limits such as postu- 

 lated by Maupas. Chejfec (1929), for example, found that the life 

 of a single individual of Paramecium caudatum may be prolonged 

 up to one hundred and twenty days by appropriate regulation of 

 the number of Bacterium coli supplied. If fertilization is an almost 

 universal phenomenon we should be able to determine the conditions 

 both within the protoplasm and in the environment which bring it 

 about. If fertilization satisfies a protoplasmic need we should be 

 able to find out what the need is. When that explanation is forth- 

 coming we shall probably be able to understand why the animal 

 flagellates continue to live so successfully without it. 



In regard to the life cycle of Protozoa we are apparently all 

 agreed on some cases. Since the classical work of Schaudinn (1900) 

 on Eimeria (Coccidium) schubergi no one doubts the general facts 

 of the life cycle in Sporozoa; his work has been confirmed by scores 

 of investigators and upon an enormous number of representative 

 species. A sequence of vital phenomena intervening from fertiliza- 

 tion to ultimate gamete formation and fertilization is characteristic 

 of all such cycles and in all cases the race comes to an end with 

 the formation of gametes, when without fertilization, the gametes 

 die. Similar cycles are characteristic of Foraminifera and wher- 

 ever gametes are formed the ultimate fate is the same. With 

 ciliates, except in rare instances, gametes are not formed but the 

 organization of the protoplasm undergoes changes at maturity when 

 fertilization processes (conjugation) occur, and in the great major- 

 ity of pedigreed cultures, the race, like unmated gametes, comes to 

 an end by natural death (see p. 282). The life cycle in all Protozoa 

 signifies the series of events between fertilization and fertilization 

 again or natural death. It involves characteristic changes in 

 organization of the protoplasm and equally characteristic manifes- 

 tations of vitality. 



I have dwelt at some length upon these experimental results, 

 and on the diverse conclusions based upon them because I believe 

 that the principle of the life cycle in Protozoa is a fundamental 

 biological concept involving changes in protoplasmic organization 

 as a result of continued metabolism. I have reason to believe, 



