CHAPTER XII 



THE HETEROGENETIC ORIGIN OF CILIATED INFUSORIA 



(a) On the Appearance of Ciliates in Infusions prepared 

 from Hay and other Plants. 



IF Ciliates are to appear in infusions of hay or other plants, the 

 infusions should be made by steeping the plants for two to four 

 hours in water at a temperature of 70-80° F. The fluid should then 

 be filtered into a clean beaker, or other glass vessel, to a depth of 

 three or four inches, through two layers of fine Swedish filtering 

 paper. The vessel containing the filtered fluid may be placed 

 under a bell- jar, or have its top loosely covered with a cap of 

 filtering paper in order to protect the surface from the advent 

 of much dust. The infusion may be either left exposed to ordi- 

 naiy daylight or placed in a dark cupboard without apparently 

 influencing the result very much, so long as the temperature in the 

 two situations remains about the same. The temperatures proving 

 most favourable for varied changes in the infusions seem to be 

 those lying between 60° and 75° F. Temperatures higher than 

 this are, as I have found, less likely to lead to the production of 

 Ciliates in the pellicles that form on most infusions. 



The fact, as I have shown elsewhere,' that Ciliates have not 

 appeared when the infusions have been made from immature and 

 living grasses, and that one kind of Ciliate, and one only, speedily 

 appeared when the infusions were made from ripe and recently 

 dead grasses, must be regarded as facts of cardinal importance. 

 It speaks against the notion of the appearance of the Ciliates in the 

 filtered infusion being due to the fact that the grasses are contami- 

 nated with such organisms either from the air or by others which 

 may have made their way up from the soil. If they had come 

 from either of these sources they should have shown themselves in 

 ' " Studies in Heterogenesis," p, 87. 



