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Experiments with Anesthetics

sense-organs, sea-water, activity, halves and regeneration

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In the previously described experiments it was shown that the active half of a medusa disk prepared as shown in figures 3 and 5 has a higher rate of regeneration than does the inactive half of the same specimen. While this point is clearly shown in all the experi ments of the two types just mentioned, the results obtained by this method throw no light upon the nature of the control exercised by the marginal sense-organs as to whether it is exerted through the higher metabolism brought about by muscular activity or through some other less apparent metabolic process under the control of the sense-organs.

Two other types of experiments were undertaken to ascertain the nature of the nervous control. In the first set of experiments (type 3) disks prepared with insulated active and inactive halves (fig. 3) were allowed to regenerate in sea-water to which 15 per cent by volume of 0.6 m had been added. In this solution the disks will live for an indefinite time and will for several hours retain the capacity to regain their normal activity within a few moments after being returned to fresh sea-water. Mayer (op. cit.) has shown that the effect of the magnesium in a weak solution in sea-water is for a time confined almost entirely to the muscular tissues, while the nervous network is still capable of transmitting the impulse necessary for pulsation over an area submerged in the magnesium solution where no contraction of the muscles could be observed. When kept in the magnesium sea-water for a prolonged period the sense-organs become incapable of giving rise to the stimulus necessary for normal pulsation long before the nervous network loses its capacity for transmitting such a stimulus, so that a ring cut from a medusa disk and activated by a circuit wave of contraction will show by an indicator strip in sea-water (Mayer, loc. cit., page 122) the transmission of the nervous impulse for some time after a ring retaining its sense-organs is no longer able to activate its indicator strip.

When medusa disks prepared with insulated active and inactive halves are put into the magnesium sea-water they lose their power of muscular movement within a few moments. Usually all of the disks

float on the surface of the new solution for 20 to 30 minutes before they become adjusted to the abnormally dense medium; at the end of this period they settle to the bottom of the jar and remain completely relaxed throughout the experiment.

During the first 12 hours of an experiment, or as soon as the newly regenerated tissue became recognizable, regeneration is more rapid from the side on which the sense-organs are present. From that time on, the regeneration from the two halves is (within the limits of error of the measurements) about equal. The rate of regeneration of the half-disk with sense-organs fails to equal that of the half-disk without sense-organs. For both halves the rate was noticeably lower than that of the inactive half of a disk in normal sea-water. The lack of proper aeration commonly brought about through the pulsation of the active half-disk may account in part for the lower rate of regeneration, but there is unquestionably some more fundamental disturbance in the metabolic activity caused by the presence of the excess of Mg ions in the fluid.

The results from experiments of this type with the halves of 40 disks is given in table 2 and is shown graphically in figure 7.

Experiments with KCN or chloroform dissolved in sea-water did not give satisfactory results. In both these solutions the tissues of the medusa underwent rapid disintegration if the amount of the reagent present was sufficient to bring about any noticeable effect upon the activity of the sense-organs.

When medusa are treated with a weak solution of oxalic acid in magnesium-free artificial sea-water it is possible to destroy the activity of the sense-organs for a considerable time without seriously injuring the other tissues. In all my experiments, however, recovery of func tional activity by the sense-organs took place within 24 hours if the oxalic-acid solution was of such a strength that the ectodermal tissues were not injured. In such experiments there was at first an equal rate of regeneration for each of the halves of a disk until the sense-organs regained their functional activity, after which the half-disk with sense organs regenerated most rapidly.

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