Effects of Temperature on Tropical Marine Animals. 7 



An even more striking case is that of the tropical reef-flat coral Sider- 

 astrcea radians, which, although it normally lives in water of 29° to 31° C, 

 can survive without apparent injury after being placed for 8 hours in water 

 at 6.7° C, and one specimen survived with some maceration of tissue a 

 temperature of 1.9° C. It is difficult to see why this coral does not invade 

 the waters of the temperate regions, but it is unknown north of Bermuda. 



The development of the ability to withstand higher or lower temperatures 

 is associated with physical changes in the protoplasm. For example, 

 Dallinger (1887), Davenport and Castle (1895), Greely (1901), McGill 

 (1908), Rautmann (1909), etc., observed that organisms when heated 

 excrete water and thus their albumens become denser and the temperature 

 of coagulation is raised. A decided congelation of the slime is observed in 

 Cassiopea which has been cooled to its non-active limit. 



In the tropical scyphomedusa Cassiopea xamachana, however, move- 

 ments cease long before heat-rigor develops, and in fact the loss of move- 

 ment is due to a general muscular relaxation, which develops several degrees 

 below the temperature at which the nerves cease to transmit the pulsation 

 stimulus. If, for example, we cut a ring (fig. i) of subumbrella tissue of 

 Cassiopea, leaving a radial strip projecting 

 from the outer side and then start a pulsa- 

 tion-wave in the ring, every time the wave 

 passes the point B a portion of the wave is 

 diverted and passes out to the end of the strip 

 BC. If, then, we place the strip BC and the 

 ring in separate dishes of sea-water, and warm Fig. i. 



the ring while the strip remains at a normal 



temperature, the amplitude of pulsation is reduced to insensibility in the ring 

 at about 38.5° C, and all the muscles are relaxed while the nervous im- 

 pulse which produces pulsation still causes the strip BC to respond vigor- 

 ously every time it passes the point B up to about 41.7" C. Thus the 

 muscles are more profoundly affected by the heat than are the nerves. 



There is another reason for the belief that heat-rigor, or at least coagu- 

 lation of albumens, is not the cause of death at high temperatures, for 

 practically no marine animals can withstand 46° C, most of them dying 

 below 40°, while the most readily coagulated emulsion of egg albumen does 

 not congeal below 56° C.^ 



Snyder (1907, Archiv fiir Anat. und Physiol., p. 113), basing his con- 

 clusions upon Nicolai's observations of 1901, came to the conclusion that as 

 many physiological reactions have the same temperature coefficient as have 

 chemical reactions, the underlying cause of the physiological reactions must 

 be of a chemical rather than a physical nature. In 1908 Snyder published 

 an extensive and important paper upon this subject in which he made use 

 of the results of all previous studies bearing upon the case; and he concludes 



' As a result of our recent experiments upon the corals of the great Barrier Reef of Queensland it 

 api)ears that high temperature causes death through asphyxiation, the oxygen of the sea- water becoming 

 insufficient to support the increased metabolism. 



