Shkldon, Rcaitioii.s to Chetmcdl Stimuli. ZJJ 



lijdrocliloride, picric acid, aiuiiioiiiuin and .sodium picrates for bitter. 

 All were made up in distilled water on the basis of the gram-molecu- 

 lar solution. The inorganic acids were prepared as normal solutions, 

 titrated against an alkali of known strength for accuracy. The 

 other solutions were made up by weight, the concentration first used 

 as a test depending partly on the solubility of the chemical used. The 

 chlorides were i)repared as 5n solutions, the sugars 3n, sodium hy- 

 droxide as n, saccharine n/0, quinine hydrochloride n/10, picric acid 

 and its salts n/15. In the experimental work all of these solutions 

 were gradually diluted until the liuiit of reaction was reached. Suf- 

 ficient time was giyen between tests at ditferent degrees of concen- 

 tration and with ditferent substances to eliminate after-eifect. 



A large number of dogfishes were used in the exj)eriments in order 

 to rule out individual yariation, ]\rost of the normal fishes used were 

 those caught in the fish traps and placed shortly in tanks about a 

 meter and a half long, two-thirds of a meter wide and a third of a 

 meter deep. A current of sea water was kept constantly running 

 through the tanks. After a few days in these tanks the fishes could 

 be handled with little difficulty. For most of the Avork, indiyidual 

 adult dogfishes were removed and placed in a smaller trough about 

 eighty cm. long, thirty cm. wide and fifteen cm. deep, through which 

 a strong current of sea water was flowing. iVfter a little handling the 

 animals would lie quietly in this trough either on the dorsum or ven- 

 ter, submitting to a certain amount of manipulation. In cases where 

 it was necessary to have part of the animal out of water or where the 

 fish was very unruly it was fastened to a frame. 



Application of the Siimulus. — The solutions were applied by means 

 of a pipette and were, in most cases, ejected slowly with the tip of 

 the pij^ette about two millimeters from the skin of the fish. In such 

 cases the fish was completely covered with water. Where it was es- 

 sential that the region stimulated should be out of water absorbent 

 cotton saturated with the solution was usmilly applied. Occasionally, 

 however, the solution was ejected directly against the skin and the 

 time of the tactile reaction taken, after which the slower chemical re- 

 action could usually be identified. In stimulation of the mouth or 

 nasal capsules a metal guard, closely fitted to the snout, was placed 



