THE EFFECT OF TEMPERATURE, FOOD, AND THE 



AGE OF THE CULTURE ON THE ENCYSTMENT 



OF DIDINIUM NASUTUM. 



S. O. MAST AND YASUSHI IBARA, 

 FROM THE ZOOLOGICAL LABORATORY OF THE JOHNS HOPKINS UNIVERSITY. 



INTRODUCTION. 



Investigations on encysted organisms clearly indicate that length 

 of life and lethal desiccation, temperature, and chemical concentra- 

 tion are greatly extended by encystment. Baker (1771) maintains 

 that the rotifer, Tylenchus, revived after it had remained in a dried 

 condition on the surface of grains of wheat for 27 years. Doyere 

 (1842) found that rotifers kept for 17 days in a desiccator, fol- 

 lowed by 28 days under the belljar of an air-pump with a pressure 

 of only 5 to 6 cm. of mercury, and thereafter thoroughly dried in 

 direct sunlight, and then subjected to a temperature of 140 C. 

 were still. viable. Mast says (1917): "Cysts of Didinium kept 

 sealed air-tight in a 10 c.c. vial for nearly five years were still 

 viable." Bodine found that the cysts of Colpoda withstand ex- 

 traordinary concentrations of various acids and narcotics as well 

 as remarkably high temperatures. 



The results obtained in observations on the cause of encystment 

 are, however, much less conclusive. Root maintains that the en- 

 cystment of suctoria is due to lack of food. He says (1914) : 

 When left without food for several weeks, Podophryae become 

 smaller and finally encyst in situ." Mast obtained similar results 

 in experiments on Didinium, but not invariably. He says (1917) : 

 " Encystment in Didinia can usually be induced at any time by 

 cutting off the food supply. But it frequently occurs when there 

 is an abundance of food present and sometimes it does not occur 

 when there is none. This is especially true for the cultures in 

 which conjugation has been prevented for a considerable number 

 of generations." Miss Carter (1919) seems to think that abun- 

 dant food is essential for encystment of Amoeba:, but that low tem- 



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