Sphaerium (Cyclas) by Gartkiewicz (1926), who 

 described the suppression of heart beat and of 

 ciliary motion during the periods of shell closui'es. 

 Because of the high transparency of the shell of 

 Sphaerium- the behavior of the heart of this mol- 

 lusk could be observed under normal conditions. 

 Gartkiewicz calls the inhibition of cardiac and 

 ciliary activity the "sleep" of the bivalves. The 

 cause of the heart's inhibition is not known; it is 

 probable that in the case of Sphaerium the lowered 

 pH of body fluids and the accumulation of carbon 

 dio.xide may have contributed to the suppression 

 of cardiac activities. This, however, does not 

 account for the observed temporary cessations of 

 heart beats in the oysters and clams kept in sea 

 water but with their valves partly removed. 

 Apparently the stoppage associated with the con- 

 traction of the adductor muscle was due to inhibi- 

 tion originated from the nervous system. 



The heart beat in 0. circumpicia of Japan 

 reaches a ma.ximum of 30 beats per minute at 35° 

 C. and slows down to three beats per minute at 

 5° C. and to 14 at 40° C. No heart action was 

 recorded by Takatsuki (1927) at 0° and at 45° C. 

 Climatic conditions apparently influence the heart 

 rhythm since it was shown by the same author 

 (Takatsuki, 1929) that the heart pulsation of 0. 

 circumpicta P. from the waters of the northern part 

 of Japan (Anomori Prefecture) is about 14 times 

 per minute at 20° C. In contrast, the pulse of (K 

 dendata Kuster from the bay of Palau, .South Sea 

 Islands, where the temperature ranges from 28° to 

 29° C. throughout the j^ear, was only eight times 

 per minute, and the ma.ximum rate of 22 times per 

 minute was observed in the laboratory at 45° C. 

 The pulsation in the northern species at tempera- 

 ture of 28° to 29° C. was 24 times per minute, and 

 the critical temperature was 35° C. These obser- 

 vations may indicate differences in thermic adjust- 

 ments of oysters inhabiting cold and warm waters. 

 No general conclusions can be drawn at present 

 from Takatsuki's observations because other fac- 

 tors such as degree of se.xual maturity and general 

 conditions of the oyster, which were not reported, 

 may affect the heart beat. 



Visual observations can be carried on for short 

 periods of time only, and their usefulness is, there- 

 fore, rather limited although their distinct ad- 

 vantage is that the heart is not affected by experi- 

 mental manipulations. The pulse curve of the 

 heart beating inside the intact pericardium may 

 be obtained by the sphygmogi-aph tambour tech- 



nique. Continuous recording may be made for 

 several hours before the heart is fatigued by the 

 weight of the wTiting lever pressing on the pericar- 

 dium wall and the rhythm and amplitude decrease. 

 The wave-line curve sllo\\^l in figure 226 repre- 

 sents the changes in the hj-drostatic pressure inside 

 the pericardium, the increase in pressure corre- 

 sponding to systolic contraction of the ventricle 

 which is followed by the falling of pressure dm'ing 

 the diastole when the auricles expand and are 

 gradually filled with blood. The method is not 

 sensitive enough to record separately the con- 

 tractions of the auricles, which beat shortly before 

 the contraction of the ventricle. In the experiment 

 shown in figure 226 the oj'ster was kept in about 

 3 1. of sea water at 22.5° C. ; its pulse rate was 18 to 

 20 times per minute. 



Figure 22G. — Pulsu of an adult C. virginica at 22.5° C. 

 recorded by transmitting the motion of the pericardium 

 membrane to the writing lever. Time interval: 3 

 seconds. 



Tlie contractions of auricles interposed between 

 the two ventricular contractions are clearly seen 

 on the tracings of the beats of an exposed heart 

 witli the hook connecting the writing lever placed 

 under the auriculo-ventricular junction (fig. 227, 

 two lower lines). In the upper line, the hook was 

 under the ventricle near the emergence of the aorta 

 and the auricular contractions were not registered. 

 The increase in frerjuency of beat shown in the 

 third (lowest) curve was due to an increase in the 

 water temperature from 20.5° to 24.5° C. 



Tracings obtained with the excised heart are 

 similar to those made by the heart in situ with 

 the hook under the ventricle since no contraction 

 of the auricles can be registered in such prepara- 

 tions (fig. 228). 



EXTRACARDIAC REGULATION 



Carlson (1905a, 1905b, 1905c, 1906a, 1906b, 

 1906c, 1906d, 1907) has shown that stimuhuion 

 of the visceral ganglion of Cardium, Ptden, 

 Mytilua, and other bivalves produces an inhibitory 

 effect on the heart. Using faradic stinuiiation, 

 Diederichs (1935) demonstrated that a single 

 shock applied to the visceral ganglion of Afytilus 

 prockices diastolic arrest. By separating the 

 ganglia he obtained evidence that both the ac- 



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FISH AND WILDLIFE SERVICE 



