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Relation Between Area of Tissue Enervated by a Single Sense-Organ and Rate of Pulsation

original, reduced, decline, tissues and disk

RELATION BETWEEN AREA OF TISSUE ENERVATED BY A SINGLE SENSE-ORGAN AND RATE OF PULSATION.

Eimer (1874) made the observation that as the area of tissue ener vated by a single sense-organ was progressively decreased there was a corresponding decline in the rate of pulsation. He states that the de cline in rate is directly proportional to the decrease in area through the range of the experiment.

Romans (1895) repeated these observations and denied the con clusion of Eimer that the decline in rate was directly proportional to the decline in area; but he did not give any definite statement of the mathematical relation between area and rate of pulsation. Mayer (1906) confirmed and extended these latter observations, but again did not accurately determine the relation between tissue area and rate of pulsation.

In my own experiments all sense-organs but one were removed from each disk, and after allowing a period of 1 hour for recovery from the shock of the operation the rate of pulsation was recorded. Immediately after this record was completed the area under the control of the sense-organ was reduced to one-half its former extent by making a cut through the subumbrella tissues. In this manner the area of tissue was reduced to 1, 4, and of that of the entire disk (fig. 16) and a record of the pulsation rate was secured for each area. In all, 141 disks were used in this series of experiments.

A summary of the results is given in tab" As will be seen from the graph, the decline in rate follows a right line very closely, except at the point where the rate for 4- the original area is shown. When extended to included areas of tissue less than of the original the decline in the pulsation-rate follows practically the same formula as shown in figure 17, by the broken line extending to a point where the tissue area under the control of the single sense-organ is reduced to the original size.

A reduction of the area of a disk beyond of the original could not be made accurately by the operation illustrated in figure 17.

When further reduction in area was desired, linear strips of constant width, each with a single sense-organ, were cut from the body of large meduste, so that the area could be accurately reduced to rig and that of the original area. The fall in rate, as recorded for the few observations made, when graphically represented produced a continuation of the straight line obtained from the larger subdivisions of the disks.

The elimination of any portion from the excitable area could be produced., by immersing that portion in a 0.4 m solution, as

shown_ in figure 18. When the anesthetizing solution was contained in:the middle vessel the nerves were capable of transmitting the impulse across this area, where the muscles were inactive, to the tissue in dish No. 3, so that the inactive area could be obtained at any point in the strip No differences in the results were obtained when the activity, of a given area of muscles was eliminated by the cutting of the subumbrella tissues or their immersion in the solution. Pieces of tissue in sea-water were found to be capable of responding to each separate induction shock when applied at the rate of 126 per minute when they had been reduced to -5-6 of the original area of the strip which represented scarcely more than rev of the area of the original disk.

This fact makes it apparent that the decline in rate of pulsation caused by reducing the area enervated by a single sense-organ is not at all dependent upon the necessity for a latent period on the part of the muscular tissues. On the other hand, there is no apparent reason why the sense-organs should be incapable of carrying on at the usual rate the chemical reaction by which sodium is liberated, unless they are depend ent upon the other tissues of the subumbrella for some substance which in the smaller areas becomes reduced to such an extent that it can no longer be produced rapidly enough to allow the sense-organ to dis charge at the usual rate.

The fact that in a nor mal medusa the initia tion of pulsation is taken up by one after another of the sense-organs at irregular intervals may indicate that, even while in normal relationship to the surrounding tissues, each sense-organ during its period of control of the pulsation of the medusa exhausts from its immediate surroundings some substance necessary for the maintenance of the discharge of impulses at a regular high rate. Since the pulsation-rate of a medusa is under normal conditions constant, each sense-organ must give up its control as soon as its power of giving out impulses falls below that necessary to maintain the usual rate of pulsa tion. When a given sense-organ has surrendered to a more active neighbor the initiation of pulsation, it will have a sufficient latent period to recover the chemical equilibrium necessary for bringing its rate of discharge of impulses up to that necessary to supplant any other center as the controlling factor in pulsation.