STIMULI AND THEIR ACTIONS 



437 



The oxygen-optimum of each species was represented very 

 distinctly by the distance of the individuals from the source of 

 oxygen (Fig. 214, / and IF). 



Among ciliate Infoisoria chemotactic phenomena have thus far 

 become little known ; nevertheless, for a few species Massart has 

 been able to demonstrate chemotactic properties toward various 

 substances. The negative chemotaxis of the infusorian already 

 mentioned, Anophrys, toward common salt may be cited ; this may 

 be demonstrated in a very simple way. Massart laid at the edge 



Fio. 214. — Chemotaxis of Baxttria (Sph-ittum) and Infusoria {Anophrys). /, Bubble of air under the 

 cover-glass, surrounded by two zones, the nearer of which consists of Anophrys, the farther 

 of SpiriUum. U, Edge of the cover-glass. Anorphrys and SptriUum form similar zones. 

 ///, Two drops of water united by a bridge of water. In the upper drop is common salt. 

 The Infusoria (Anophrjfs) in this drop wander over into the drop of pure water, the more the 

 salt disaolves. (After Maasart.) 



of a drop in which numerous specimens of Anophrys existed a few 

 small crystals of common salt, and connected the opposite side of 

 the drop bv a narrow bridge of water with a similar drop of dis- 

 tilled water (Fig. 214, III). The result was that the Infusoria fled 

 from the spot where the salt lay the more, the more the salt dissolved 

 and diffused into the neighbourhood, until finally they had all passed 

 over the narrow connection into the other drop. 



Jennings ^ has recently made very comprehensive and systematic 

 investigations of the eheinntaxis of Z'(7?-(';;(rt'('/((«(,and has employed 

 a method that possesses in many respects great advantages. 



' H. S. Jennings: "Studies of reactions to stimuli in unicellular organisms. 

 I. etc.," Jourji. of Physiol., 1S97, xxi. , p. i^S. 



