FUNCTION OF LATERAL-LINE ORGANS IN FISHES. 195 



behaved a- though they were in ordinary sea water, and hence the general condition 

 of foul water could not he said to affoi'd a stimulus for the lateral-line organs. 



Salts, food substances, oxygen, carbon dioxide, and the materials in foul water 

 would probably all act as chemical stimuli on the lateral-line organs, if they acted at 

 all, hut since none of them appear to be stimuli for these organs, the observations of 

 Bugnion (1873), Fuchs (1894), and Nagel (1894) to the effect that the lateral-line 

 (Means are not stimulated chemically, were confirmed. This view of the nonchemical 

 reactiveness of the lateral-line organs has been clearly maintained from a morpho- 

 logical standpoint in two recent papers by Herrick (1903a. L903b.) 



Pressun of watt /'. — Fuchs (1894, p. 474) suggested thatchanges in the hydrostatic 

 pressure might be the means of stimulating the lateral-line organs. In testing this 

 proposition normal and cut individuals of Fwidtdus heteroclitus were subjected to 

 diminished hydrostatic pressure in a cylindrical "lass museum jar three-fourths full 

 of water. The jar was aboul so cm. high and 25 cm. in diameter, and was provided 

 with an air-tight top. By means of a small hand pump air contained after the jar 

 was closed was removed until the pressure was reduced from the usual 15 pounds 

 per square inch to about 5 pounds. 



When the fish were first put into the jar they all descended, as is usual, to the 

 bottom, but after the removal of air had continued for some time they came to 

 the top of the water, and when the pressure had fallen to about 5 pounds, it was 

 evident that they were unable to keep below the surface of the water without vigor- 

 ous and continuous swimming. Since they possess air-bladders, it seemed likely 

 that the reduced pressure had caused such an enlargement of these organs that the 

 tish were carried to the top of the water by their own buoyancy, and this explana- 

 tion was tested by inserting capillary glass tubes into the sides of several, so that as 

 the pressure was reduced the air could escape from the bladder. When the fish were 

 subjected to diminished pressure under these conditions, air was seen to escape from 

 them, and they remained quietly swimming at the bottom of the jar. Evidently the 

 first set of fish were kept near the top of the water through their altered specific 

 gravity. Normal and cut fishes reacted in essentially the same way in these experi- 

 ments, hence there was no reason to suppose that a diminished hydrostatic pressure 

 was a stimulus to the lateral-line organs. 



In a similar way normal and cut fishes were put in a water-tight jar in which the 

 pressure could be raised from 15 to 22 pounds on the square inch. When first 

 introduced the fishes went to the bottom, and after the pressure was put on they 

 remained there with the exception of short intervals, when by vigorous swimmiug 

 they could get into the upper part of the jar. From such situations, however, they 

 would often almost drop to the bottom. As in the experiments with reduced pres- 

 sure, so here the air-bladder doubtless played a controlling part; for when it was 

 punctured so that with increased pressure water could enter it, the fish swam much 

 more freely. The increased pressure, nevertheless, stimulated the fishes, for they 

 never seemed to come into a restful state in the fifteen minutes or so during which 

 they were under pressure. Since the reactions of the normal and cut fishes were 

 indistinguishable, however, there was no reason to suppose that increased hydro- 

 static pressure is a stimulus for the lateral-line organs. 



