68 PROCEEDINGS OF THE AMERICAN ACADEMY. 



acetic acids. The degree of dissociation of these acids diminishes in 

 the order named, hydrochloric acid being most and acetic acid least 

 dissociated. 



The strength of these solutions was so chosen that they should give 

 distinct and measurable reactions, not sufficiently strong, however, to 

 produce in any case lasting injurious effects upon the worm. Prelim- 

 inary trial showed that an —^ solution was serviceable for this pur- 

 pose, since at higher concentrations the acids were so stimulating that 

 the worms withdrew within two-tenths of a second, and, consequently, 

 it was impossible to state whether at these concentrations one acid 

 was a more effective stimul :s than another. 



The method of handling the worm was, with few modifications, like 

 that used by Parker and Metcalf (: 06) in their study of the reactions 

 of earthworms to salts. The worms were thoroughly rinsed in tap- 

 water till they were cleaned externally of foreign matter, and each 

 worm was suspended by a silk thread passed through the posterior tip 

 of its body and loosely tied. The worms thus prepared and numbered 

 were kept singly in small, open, glass vessels lined with moistened filter 

 paper, upon which the worms were allowed to crawl. The method of 

 keeping them in tap- water was found undesirable because the water 

 seemed to excite the secretions of mucus with the result that the mu- 

 cus thus formed prevented the easy penetration of the acid to the skin 

 of the worm and made the reaction -times slow and unreliable. The 

 filter paper, on the other hand, served to remove all excess of mucus 

 from the worms. 



The apparatus with which the tests were made consisted of a base 

 with an upright wooden post to which a pivoted arm was fixed. One 

 of the ends of the arm was notched so that the silk thread carrying a 

 worm could be inserted into it, and the other end was used as a handle 

 by which the arm could be moved so as to raise the worm or lower it 

 into the solution contained in a glass vessel on the base. When a test 

 was to be made, a worm was taken up by its thread and attached to 

 the arm of the apparatus. The superfluous water was drained from it, 

 and, after it had lengthened fully, it was lowered gently, but quickly, 

 into the solution to the depth of the anterior edge of the clitellum. 

 As the tip of the worm cut the surface of the solution, a stop watch 

 was started, and when as a result of the contraction of the worm, the 

 tip withdrew from the solution, the watch was stopped. The interval 

 of time thus recorded to fifths of a second was taken as the reaction- 

 time for that particular experiment. If the worm failed to react after 

 two minutes, the experiment was discontinued, and the worm was taken 

 out of the solution. Such extremely long reactions were common 



