<Z)- 



Centimeters 



Figure 223. — Method of obtaining tracings of oyster heart 

 in situ. ad.m. — adductor muscle; h. — glass hook under 

 the ventricle, V; w.l.— water level. The upper valve 

 has been removed, the pericardium dissected, and the 

 oyster placed on a suitable base in a finger bowl. 



both ends and the organ is placed in the perfusion 

 chamber filled with sea water or with Ringer 

 solution. The aorta end of the heart is connected 

 to the writing lever, and the auricular end is 

 attached to the base. The chamber is a glass 

 tube about 2 cm. in diameter with an overflow 

 arm near the top (fig. 224). The length of the 

 tube may be adjusted to obtain the desired 

 volume, usually 10 or 20 ml., between the bottom 

 and the overflow. The liciuid (perfusate) is 

 delivered through an inlet A at the bottom; it 

 fills the chamber to the level of the overflow and 

 runs out through outlet B. The preparation 

 may be aerated through a second glass tubing 

 inserted in the bottom. Under this condition 

 the heart remains alive and active for several 

 days. 



A very delicate technique to study the nerves 

 which stimulate the oyster heart {0. circrimpicta) 

 was developed by Oka (1932). The preparation 

 was made in the following manner: the shell was 

 carefully cut off without any injury to the peri- 

 cardial region and visceral ganglion, the greater 

 part of the gills with the mantle were removed; 

 the adductor muscle was dissected; and the 

 oyster was fastened to a small board in the manner 



248 



shown in figure 225. In this way the visceral 

 o-andion with its nervous connection and the 

 heart were exposed and made accessible for stimu- 

 lation. The heart was kept in water, but the 

 ganglion was e.xposed to air. The rhythm was 

 recorded for the heart in situ and separately for 

 the ventricle and two auricles. For the latter pur- 

 pose the heart was cut at the auriculo-ventricular 

 junction and the cut end tied with a silk thread. 

 The free end was connected to a writing lever of 

 a kymograph (upper right part of figure 225). 



FREQUENCY OF BEAT 



The heart beat of all bivalves is so gi-eatly 

 affected by the envu'onment that reports of the 

 rates of beat are of little value unless the conditions 

 under which the observations were tnade are 

 completely and accurately described. Frequency 

 of heart beat increases with the rise of temperature 

 and decreases with its fall. According to Federighi 

 (1929), the response follows Arrhenius equation 

 from which the so-called temperature coefficient 

 (designated as ju) can be calculated, using the 

 technique developed by Crozier. Discussion of 

 temperature characteristics of biological processes 

 in general and the application of the Arrhenius 

 equation of the effect of temperature on chemical 

 reactions to heart physiology is beyond the scope 

 of tliis book. The reader interested in the problem 

 is referred to Barnes' (1937) Textbook of general 

 physiology, chapter XIII, or to chapter I in 

 Crozier and Hoagland's (1934) Handbook of 

 general experimental psychology. There is, how- 

 ever, serious reason to question the validity of 



PERFUSATE 



OUTLET 



Centimeters 



Figure 224. — Wait's perfusion chamber for recording the 

 activity of an excised heart of mollusks. From Wait, 

 1943. 



FISH AND WILDLIFE SERVICE 



