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Production Influence of Sense-Organs on the Rate of General Metabolism as Measured by Co

experiments, sea-water, experiment, time and volume

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The results of the experiments recorded in the two preceding sections show that the nerve-centers exert a decided influence on the rate of metabolic activities when measured by two different standards. It seems apparent also that, although the standards of measurement adopted—regeneration and loss of weight during starvation—largely involve the activities of distinct tissues, the influence of the organs is exerted in a manner strikingly similar in the two cases. This similarity in result suggests the probability that the effects measured h nnr nhataasi of the general metabolic activity of the organism, which when measured as a whole would show an influence of the nerve centers comparable to that obtained when the activities involved in distinct functions are used as the unit of meas urement.

The measurement of the amount of carbon dioxide given off by a half-disk within a given space of time affords means of determining the comparative rate of total metabolic activity of speci mens under the operative conditions used in the previ ous experiments. The tech nique of the experiments was as follows: The half-disks were prepared in the manner previously described, so that active, activated, and inac tive individuals were secured for comparison. Each half-disk of any pair was placed in a separate jar containing about 1,200 c.c. of fresh sea-water brought from the ocean at the time of beginning a set of experiments. The capacity of the jars varied slightly and pairs of equal volume had to be selected for the two halves of the same disk.

As the measurable amount of

produced and consequently the rate of pulsation for some time after the beginning of an experiment were largely dependent upon the activity of the zooxanthellm, most of the experiments were started late in the afternoon and therefore continued during the hours of darkness. When experiments were going on during the day the necessity for covering the jars with dark cloth caused a decided rise in temperature, which increased unneces sarily the complication of the calculations involved in determining the amount of given off in respiration.

Preliminary experiments along this line were undertaken, in collabo ration with Dr. S. Tashiro, in 1915, when the determinations were

made by means of titrating the sea-water with n/100 NaOH, using phenolphthalein as an indicator and titrating to the color obtained by adding the same amount of indicator to an equal volume of sea-water taken as a control at the beginning of each experiment.

In the later experiments the amount of

given off by each half disk was determined by ascertaining the P. (minus log hydrogen-ion concentration) of a sample of sea-water taken as a control at the beginning of the experiment, and that from the jar in which the speci men had been respiring during the experiment. Both specimens involved in an experiment were removed from the jars at the same time, whenever the determinations were to be made or either specimen had ceased pulsating. The volume of necessary to bring about a corresponding change in the hydrogen-ion concentration of an equal volume of sea-water (1,200 c.c.) was determined by adding known volumes of to that volume of sea-water.

The results of these determinations are shown in figure 13. This result confirms McClendon, who shows that the content of sea water can be more accurately measured by determining the hydrogen ion concentration than by a direct determination of the CO,.

When the half-disks were placed in the closed jars the increase in the hydrogen-ion concentration of the sea-water caused at first an increase in their rate of pulsation. This was followed after 3 or 4 hours by a gradual decline in rate until finally both activated and active half disks had been completely narcotized by the which they had themselves given off. The decline of the rate of activated half-disks was very regular and the pulsations became gradually weaker, until scarcely discernible before entirely ceasing. The active specimens, on the contrary, behaved very erratically. Frequently when the pulsation had become very slow, or had even ceased for several minutes, these specimens would suddenly take up rapid pulsation and for a short time their activity would be even greater than when under the influence of the first stimulating effect of the increased hydrogen-ion concentra tion in the early part of the experiment.

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