GALVANOTAXIS AND CHEMOTAXIS 519 



the current by shifting the rocker; the animals again turn into line with 

 the stream and generally collect about the cathode. This may be 

 repeated a few times, but after a time a toleration of the stimulus sets 

 up in the tadpole and the reaction is less certain. A young crayfish works 

 more regularly than does a frog-tadpole in the reaction to galvanism. 



The v various tropisms or taxes (of which galvano-tropism or galvano- 

 taxis is only an example) are the reactions which plant-protoplasm and 

 little-differentiated animal protoplasm exhibit when subjected unilaterally 

 to various external natural influences. Besides reacting to galvanism, 

 such protoplasm reacts among other things to light (phototaxis), to heat 

 (thermo taxis), to chemicals (chemotaxis), to pressure (barotaxis, of 

 which the reaction to contract with solid bodies, thigmotaxis, is a sub- 

 division). One sees phototaxis in many infusoria, as also in plants when 

 the leaves twist around to face the light. It is supposed that it is by the 

 force of chemotaxis that the spermatozoa are attracted to the ova. Thig- 

 motaxis is well seen in the twining of the tendrils of many vines about a 

 small support. (See Verworn.) 



Explanation of these reactions as a whole is difficult and at present 

 doubtful in most cases. One has to say that they depend on inherent 

 properties of protoplasm acquired for their usefulness. Some of the 

 reactions can be explained on purely physical and chemical principles. 



Jennings has studied these interesting phenomena in Paramecium 

 with great industry and some explanatory success. The simpler the 

 organism the more constant the reaction, for the individual will is least 

 powerful in the lowest forms of life. On this principle even young 

 frog-tadpoles show a less uniform reaction than would, e. g., paramecia 

 or amebse; dogs or men might exhibit none. 



Expt. 90. Chemotaxis. (Apparatus: Pure culture of Paramecia, 

 wide slide, large cover-glass, wires, fine pipet, carbon dioxide.) Place a 

 large drop of the water containing the paramecia in the middle of the 

 slide, and put wires about 3 cm. apart across the slide on either side of 

 the drop. Place a cover-glass on the water and see that the latter fills 

 as much of the space as possible. Observe with the naked eye or with 

 the biconvex lens that the infusoria are evenly distributed through the 

 water. Now with the pipet force a single small bubble of air under the 

 cover-glass, and then, at least a centimeter away, a tiny bubble of carbon 

 dioxide. The paramecia soon congregate in a ring about the carbon 

 dioxide. This genus of animal, then, is positively chemotactic to weak 

 carbonic acid, as it is to most other acids (Jennings). As the gas more 

 and more dissolves in the water, its solution becomes stronger and the 

 animals soon, move away from it i. e., they are negatively chemotactic 

 to strong carbonic acid. 



It is this sort of attraction perhaps which causes the spermatozoa to 

 enter the ovum, being aided in their ascent of the tubes possibly by 

 another sort of taxis, rheotaxis, or reaction against the current of lymph 

 setting toward the uterus. 



