INFLUENCE OF SENSE-ORGANS ON THE CHANGE IN RATE OF PULSATION IN RESPONSE TO CHANGES IN TEMPERATURE The studies of Harvey (1911) and Mayer (1913) have shown that when Cassiopea is slowly heated the rate of nerve-conduction increases from about 18° C. to about 36° C., after which there is a rapid decline in the rate. Recovery of the medusa is impossible if the temperature is carried much above 40° C.; indeed, when cooling is begun before a fatal temperature is reached the normal rate of pulsation does not return even when the me dusa has been kept at normal temperature for several days. In its general features the curve for the rate of nerve conduction in Cassiopea re sembles that for enzyme ac tion, as was pointed out by Harvey, and as shown for the pulsation-rate of the verte brate heart (Knowlton and Starling (1912) et al.).
Since Mayer (1908) has shown that the initiation of the stimulus for pulsation takes place in the sense-organs through a definite chemical reaction, it was thought possible that if a sense-organ were subjected to changes in temperature while the body of the disk was kept at a constant temperature, the resulting rate of pulsation might follow Van't Hoff's 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 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 in 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.
The pulsation-rate of active specimens frequently reached its maximum at from 27° to 29° C. In other specimens the maximum rate was not attained until a temperature of 37° C. had been reached, after which the decline in rate was precipitous, death occurring at 38.5°.
A summary of all the results is given in figure which shows the average for 11 active and 9 activated half-disks.