Centimeters 



Figure 225. — Oka's method of exposing the visceral ganglion for study of heart stimulation in the oyster. Reproduced 



from Oka, 1932. 



tlie underlying theory of temperature coefficients 

 of biological reactions (Belehradek, 1935). 



In experiments with C. in.rginica at the Woods 

 Hole laboratory Federighi (1929) found the values 

 cif M equal to 16,000 and 1.3,600. It is rather 

 difficult to convert his data into conventional 

 terms of number of beats per minute since his 

 experimental results are presented only as plots 

 of logarithms of the frecjuencies (time required for 

 10 beats) multiplied by 100 against the reciprocals 

 of absolute temperature. x\t my request Federighi 

 in a personal communication supplied excerpts 

 from his laboratory notes which show the following 

 rates: 



The rates appear to be much higher than those 

 observed by others. In Federighi's experiments 



the upper critical temperature above which there 

 was rapid decline in pulse rate was approximately 

 30° C. 



In Koehring's (1937) observations on C. irirgin- 

 ica the heart rate averaged 20 beats per minute at 

 20°. She found also that in the oysters with one 

 valve completely removed the heart action was 

 inhibited for several hours and there was no ciliary 

 motion of the gill epithelium. Inhibition of the 

 heart's activity when the shells are closed was 

 reported by Stauber (1940) in oysters uninjured 

 except for perforation of both valves. He found 

 that the heart rhythm of C. virginica slowed down 

 and became irregular when the oyster closed the 

 valves. In some of the closed oysters the heart 

 remained inactive for 2 to 3 minutes, then resumed 

 beating at low frequencies of about two to three 

 times per minute, only rarely exceeding six beats 

 per minute at the temperature of 17.5° C. As 

 the valves began to open, the heart beat increased 

 to 14 to 16 times per minute. These results are 

 in accord with observations on Anodonta and 



CIRCULATORY SYSTEM AND BLOOD 



249 



