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The Relation of Muscular Activity to the Rate of Metabolic Processes in Cassiopea 1

trophic, nerves, function, activities and impulses

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THE RELATION OF MUSCULAR ACTIVITY TO THE RATE OF METABOLIC PROCESSES IN CASSIOPEA.

(1) The relation of muscular activity to the rate of regeneration has been considered in the section dealing with the regeneration experi ments and will be here taken up only in making comparison with the results obtained by other methods. It appears to be clearly established that in this organism muscular activity plays a relatively unimportant part in controlling the rate of metabolism as measured by the total CO: output or by either of the two other standards of measurement employed. The relatively small difference between activated and inactive specimens as measured by either of the three standards may be accounted for on the ground of differences in temperature induced by the extreme activity of the muscular system. While no estimate of the amount of heat generated through muscular activity is available for Cassiopea, the evidence secured from the study of the change in rate of nerve-conduction (pulsation) indicates that a relatively small tem perature increase would be sufficient to account for the observed differences. In spite of this temperature effect, activated disks, pulsat ing at from 3 to 10 times the rate of active specimens, show metabolic activities (by whichever of our three standards measured) considerably lower than do the other halves of the same original disk, the activities of which are under the control of the sense-organs.

(2) With the elimination of muscular activity as an important determining factor in metabolic activity there remains to be con sidered the nature of the nervous control over metabolic activity. After 1851 (when Ludwig proved the existence of nerves producing activity of the cells of secreting glands) it was held for some time that there were nerve-fibers presiding over other metabolic activities, as growth and repair. With the increasing knowledge of the part played by chemical excitation in controlling many activities, the concep tion of the trophic function of nerves, in the broader sense, has been discarded by most modern students of physiology.

The trophic function in the special sense of Heidenhain (1858) has been clearly demonstrated by the researches of Babkin (1913) for the nerves of cranial origin to certain gland-cells.

Most studies on the trophic effect of nerves on growth or other general metabolic phenomena have given negative results. Jacobson (1910) concluded, from experiments on pigeons and dogs, that the denervated areas healed as rapidly as those with the normal nerve supply. Tschermak (1910), after extended researches and a critical

review of the literature on trophic and tonic innervation, states that there is no evidence for the existence of separate or specific trophic nerves. He considers it probable, however, that motor and sensory nerve-fibers convey trophic impulses as an accessory function, which would imply the necessity of qualitative differences in the impulses which traverse any fiber. On the other hand, the work of Head and Campbell, on Herpes zoster, supports the conception of a trophic function of nerve-fibers. In this disease the presence of change in the dorsal root ganglia causes abnormal impulses to be sent in an efferent direction along the sensory fibers of the skin. On account of this excitation, blistering of the skin takes place over the area of distribu tion of the fibers (axons) terminating in the affected ganglia.

Jacobson (loc. cit.) states that "in the lower animals the main tenance of life processes are largely a phenomenon of chemical coordina tion," and that trophic influences ought to be greater in the higher than in the lower animal phyla. Her own experiments showed, in her opinion, that there was no difference in this respect between pigeons and dogs, both animals giving negative results.

Among the lower invertebrates, in Cassiopea (and in this respect it is unlikely to differ markedly from other scyphomedusre) the general metabolic activities, including regeneration (a form of growth), total production, and the using of body-substances for metabolism when no food is being taken, are strongly influenced by the condition of presence or absence of some sort of impulses from the sense-organs (nerve-centers). That there are neurones which are specific conductors of trophic impulses as distinct from motor or sensory nerves is by no means implied by this statement. In fact, in a nervous system such as that of the medusa it is not always possible, on morphological grounds alone, to separate those neurones which are sensory from those of a motor function. In the absence of even this means of establishing the identity of the character of a portion of the neurones it is useless to attempt, in the present state of our knowledge of the anatomy of this nervous system, to make any distinction between the character of the function of any particular portion of it.

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