Artificial Production of Spores in Monas 



but made no experiments to show that a lowering of the temperature itself will actually 

 cause the plant to form spores. He apparently had in mind only the limits of tem- 

 perature at which spore formation may take place, when the process is initiated by 

 other means. Beyond these observations, which are rather inconclusive so far as the 

 Protozoa are concerned, nothing is known about the conditions which determine 

 encystment or spore formation. 



Dr. Loeb suggested that I take up the problem of asexual reproduction from an 

 experimental point of view. Many authors had noticed that the mode of reproduc- 

 tion changes in certain aquatic animals or Protozoa when the pond in which they live 

 begins to dry out. But the question was: How can the lack of water in a pond inter- 

 fere with the mode of reproduction? Dr. Loeb's idea was that the real physical factor 

 at work in this case was the rapid, or extensive, changes of temperature. As long as 



■ •.••»io«-^ V * ' •* •*» -•^.— - — ■ " 



fig. 1. THE ADULT MONAS 



the bulk of water in a pond is large, the daily changes of the temperature of the air 

 will cause only a slow or slight variation in the temperature of the pond. But when 

 the bulk of water is small, the temperature of the latter will follow sudden changes in 

 the temperature of the air more rapidly and completely. In order to test this idea, he 

 suggested that I try whether or not, through sudden changes of temperature, organ- 

 isms might be caused at any time to reproduce asexually instead of sexually. The 

 experiments were first performed on Stentor, with the results already described in a 

 previous paper." It was found in these experiments that by lowering the temperature 

 the animal would go into a resting stage, which in appearance resembled a cyst ; but 

 in no case did I obtain spores. These results could not be obtained by raising the 

 temperature. 



During the past year the low-temperature experiments have been continued on 

 several other Protozoa, and in all of them structural changes similar to those already 

 described for Stentor have been obtained. But in one form, Monas, our original pur- 

 pose has been carried out, namely, the artificial production of spores by means of 

 variations in the temperature. 



Monas is a small fiagellated Infusorian, of an exceedingly simple structure, and 

 occasionally appears in great numbers in cultures that have been prepared for Para- 

 moecia. It can be easily maintained in the laboratory in great quantities by adding 

 to the culture from time to time a little bread, upon which the Monads thrive surpris- 

 ingly. In all the experiments the Monads were isolated in small, covered dishes, and 

 the supply of water kept constant by frequent renewal from the aquaria in which the 

 animals had been reared. The temperature was lowered to the desired point by placing 



6GKEELEY, American Journal of Physiology, Vol. VI (1901), p. 122. 



74 



