164 Papers from the Department of Marine Biology. 



GENERAL DISCUSSION. 



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 

 CO2 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 metaboUc 

 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 



