THE INFLUENCE OF SURFACE EVAPORATION. I I/ 



parts of the film, except the edges, were free from infusoria, while 

 dense clusters had been formed along the edges farthest from 

 the supported end. When a 6N solution of methyl alcohol was 

 used instead of a 5 A 7 " solution the effect was more marked and 

 appeared more quickly. 



Ethyl Alcohol. i c.c. of a 5 A" solution of C 2 H 5 OH was added 

 to 5 c.c. of culture. The same effect was obtained as with methyl 

 alcohol, but it was slightly less marked and took longer to appear. 



Propyl AlcoJiol. jj-A 7 " C 3 H,OH was too toxic the organisms 

 being killed too soon to obtain any result but in -y^A 7 , which 

 is about the strongest solution they will stand, there was no 

 attraction to the edges of the film. 



Ethyl Acetate. i c.c. of a saturated aqueous solution of ethyl 

 acetate was added to 5 c.c. culture. The organisms were at 

 first uniformly distributed they then showed marked attraction 

 for the edges of the film, particularly for those edges most remote 

 from the supported end and in a few minutes all the infusoria 

 were congregated at the edges at the shallower end of the film 



Calcium Chloride. i c.c. of a fA 7 " solution of CaCL was added 



O 4 



to 5 c.c. of the culture attraction to the edges was observable 

 for a short time. As in the other cases the edges farthest from 

 the supported end became the most densely populated. 



Potassium and Sodium Hydroxides. In my experiments on 

 Chemotaxis and under the conditions of those experiments I 

 obtained a marked, though more or less transient, attraction to 

 the edges of the film at a concentration of A 7 "/ 5,000. 



All the above results hold equally for Colpodinm and for Para- 

 maecium. 



In all cases the attraction to the edges finally disappeared - 

 with ethyl acetate the effect passes off in about half an hour. 



All these substances which I have found to cause aggregation 

 of the infusoria at the edges of the film are substances the solu- 

 tions of which tend to become more dilute on exposure to the 

 atmosphere. Methyl alcohol, ethyl alcohol, and ethyl acetate 

 evaporate more rapidly than water while CaCl 2 , KOH and NaOH 

 are well known absorbents of water-vapor. There is also a gen- 

 eral correspondence between the rate at which the volatile sub- 

 stances evaporate and the intensity of the effect which they pro- 



