480 



BIOLOGY OF THE PROTOZOA 



given proper conditions the protoplasm of Actinophrys has the 

 possibiHty of indefinitely continued life and reproduction by division. 

 In these exceptional cases we meet indeed with diverse experi- 

 mental results and diverse conclusions. Granted that the experi- 

 mental work in all cases is done with an equally conscientious 

 regard for controls and pitfalls of all kinds, it is necessary to accept 

 the conclusions on their merits and endeavor to find an explanation 

 which will bring them all into harmony. The first difficulty comes 

 in connection with the pojjular conception of an abnormal condition 

 of the environment. ICxcept with parasites it is obviously impos- 

 sible to study the life history of an organism under normal environ- 

 mental conditions in Nature— in all probability there is no constant 

 "natural" enviroimient. To Enriques, Baitsell, Dawson, Belaf, 

 Chatton, Jollos, and Woodruff in part, the culture methods employed 

 for ciliates are "abnormal" and death is a result of these conditions. 

 With Uroleptvs mohilis in mind it is difficult to understand by 

 what process of reasoning the conditions of the environment are 



Fig. 201. — Vitality graph of Actinophrys sol. (After Belar.) 



responsible for the decline of A'itality and death when two indi- 

 viduals from such cultural material are restored to full vitality 

 and in the same medium upon conjugation. The conditions are 

 identical for parent protoplasm and offspring protoplasm and yet 

 the former dies, the latter lives until a corresponding age, and dies 

 in turn. The more than one hinidred and twenty series that have 

 followed one another since 1917 in the same medium and under the 

 same conditions in the same rhythmical cycles and with surprising 

 uniformity furnish strong evidence that the environmental condi- 

 tions have been suitable or "normal." For each series there has 

 been the same sequence of physiological conditions— high vitality 

 and sexual immaturity, encystment power, sexual maturity, decline 

 in vigor and ultimate death. If these phases of vitality are normal, 

 if encystment and reorganization, and conjugation, are normal 

 phenomena in the life history of a ciliate then the conditions under 

 which they occur must likewise be normal. A hypercritical mind 

 may deny the existence of conjugation in Nature and maintain that 

 conjugation occurs only under the abnormal conditions intro- 



