JIOVEMENTS, ETC., OF ERESH-WATEH PLANARIANS. 643 



6. The softened food is taken into the body through the 

 pharynx. 



7. The animal spontaneously stops feeding after a certain 

 time. 



The question now arises, if the normal process of getting 

 food is at bottom in the majority of cases a reaction to a 

 chemical stimulus, what is the nature of the chemical sub- 

 stance causing it ? Can the same response be induced by 

 the use of different inorganic and organic chemicals ? Is 

 there any relation between chemical composition and the 

 intensity or form of the reaction ? To answer these and a 

 number of other questions arising out of them recourse must 

 be had to experiments in which the nature and concentra- 

 tion of the chemicals affecting the organisms may be con- 

 trolled. All the experiments of this kind I will group 

 together under the heading — 



h. Reactions to Chemical Stimuli — Chemotaxis. 



1. Reactions to Localised Chemical Stimuli. — 

 This particular phase of the general subject of the effects of 

 chemictils may be considered first, since it is most closely 

 related to what has preceded on the food reactions. The 

 plan of the experiments was to try the effect of a series of 

 substances when applied to restricted areas of the body. A 

 sufficiently large number of chemicals were used to include 

 representatives from each of the main groups of substances 

 which have been found to have marked effects on organisms. 



a. Methods. — The method which was found to give the 

 most satisfactory results in the application of localised 

 chemical stimuli was the use of a capillary tube filled with 

 the solution whose effects it was desired to test. The form 

 of the tube used is shown in Fig. 32. The tubes were 10 to 

 15 cm. long, and were made from glass tubing of about 

 2'5 mm. internal diameter. Each end was drawn to capillary 

 fineness, and then broken off so as to give an opening of the 

 desired size. The opening at the upper end was made 



