160 



Papers from the Department of Marine Biology. 



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constant temperature, the resulting rate of pulsation might follow Van't 

 HofFs law more closely than when the entire disks were subjected 

 to the change in temperature, or the rate of pulsation nerve-conduc- 

 tion of activated disks under similar conditions was measured. Such 

 experiments showed, however, that the results from this cause were 

 in no essential different when either a single sense-organ, an " active" 

 disk, or activated disk were subjected to the changes in temperature. 

 All my later experiments 

 were therefore confined to 

 those in which active and 

 activated halves of the 

 same medusa disk were 

 subjected to the tempera- 

 ture changes at the same 

 time in order to determine 

 the influence of sense- 

 organs upon the response 

 to changes in temperature. 

 The prepared half-disks 

 were placed in a 4-liter jar 

 of fresh sea-water which 



.3 



70 



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5 10 15 



cc. CO? added to 1200 cc. sea-water 



20 



FIG. 15. Showing change in hydrogen-ion concentra- 

 tion when a known volume of carbon dioxide is 

 added to 1,200 c.c. of Tortugas sea-water. 



was in turn contained in 



a 20-liter jar of fresh water 



supported on a copper tray 



filled with water. The 



water surrounding the 



inner jar was cooled by 



the addition of ice or 



heated by the flame of a small alcohol lamp so that a change of 1 



in the temperature of the sea-water was obtained hi 15 minutes. The 



activity of the medusa? was sufficient to agitate the water to such an 



extent that at no time could a difference of 0.1 C. be detected in the 



temperature of any two portions of the contents of the jar. 



In beginning any experiment the temperature was lowered to the 

 desired starting-point and then raised until either the desired upper 

 limit was reached or continued until the disks became inactive. On 

 being cooled below 20 C. the activated specimens often ceased 

 pulsating and could not again be aroused to steady pulsation by the 

 application of repeated stimuli until the temperature had been raised 

 to about 22 C. From 23 to 33 C. the increase in rate of pulsation 

 for activated specimens followed a right line (fig. 14) and within that 

 limit the rate was nearly doubled. The active half-disks, over the 

 same range of temperature, gave generally a smaller increase in rate 

 and the change in rate was always more erratic than that shown by 

 those deprived of their sense-organs. (Fig. 14.) 



