VITALITY 



257 



proof of fertilization in the entire group. On the other hand, there 

 have been no successful attempts to cultivate such flagellates by 

 the isolation culture method so that we are entirely uninformed as 

 to the relative vitality in a life cycle. It is possible that processes 

 analogous to endomixis in ciliates take place during encystment 

 stages but as to this we are also ignorant. With these exceptional 

 cases, therefore, we must wait for further information. 



Exceptional cases are increased through Belaf's observations on 

 Actinoyhrys sol, a heliozoon (1924). A single line of his main 

 culture was followed through 1244 generations by division during 

 two years and eight months. Fertilizations were obtained from 

 time to time in mass cultures, but these were prevented in the 

 isolation cultures, the latter showing no indication of reduced 

 vitality with continued life (Fig. 134). Belaf also concludes that, 

 given proper conditions, the protoplasm of Act'vnophrys has the 

 possibility of indefinitely continued life and reproduction by division. 



Fig. 134. — Vitality graph of Actinophrys sol. (After Belaf.) 



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 popular conception of an abnormal condition 

 of the environment. It is obviously impossible to study the life 

 history of an organism under normal environmental conditions in 

 Nature— in all probability there is no constant "natural" environ- 

 ment. 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 Uro- 

 Irptus mobilis in mind it is difficult to understand by what process 

 of reasoning the conditions of the environment are responsible for 

 the decline of vitality and death when two individuals from such 

 cultural material are restored, upon conjugation, to full vitality 

 in the same medium. The conditions are identical for parent 

 protoplasm and offspring protoplasm and yet the former dies, the 

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