f\j\f[l\jV[M\[\!\imiWyw^ 



Figure 230. — Tracings of the heart beats (in situ) of C. 

 virginica in sea water (upper line) and after the addition 

 of eserine, (second line) in concentration of 10^*, to the 

 pericardial chamber. Temperature 21.5° C. Time 

 interval, 5 seconds. 



drug in heart physiology is the fact that it prevents 

 the destruction of acetylcholine by the enzymes of 

 the organism. 



Veratrine has a temporaiy stimulating effect on 

 the heart of 0. edulis (Jullien, 1936a). In my 

 experiments with isolated heart of C. drginica, a 

 slight stimulating efl'ect on the frequency of 

 ventricular contraction was recorded in the con- 

 centration of veratrine of 1:10,000. Within a 

 few seconds tlie number of beats increased from 1 2 

 to 18 and 20 times per minute at 20.5° C. (fig. 231). 

 Navez (1936) described the depressive action of 

 pilocarpine on the heart of Anomia. 



High concentrations of curare inhibit the heart 

 activity of the oyster; in lower concentrations the 

 drug has a strong positive tonotropic effect 

 (Jullien, 1936a) and also counteracts the inhibitory 

 effect of acetylcholine. Jullien found that heart 

 action stopped by acetylcholine was restored by 

 subsequent applications of curare. 



Adrenaline accelerates the heart beat of 0. 

 circumpicta, (Takatsuki, 1933) in a concentration 

 of about 1.8 times 10"'. Similar activating action 

 has been reported for C. virjiinica (Otis, 1942) and 

 for 0. edulis (Jullien, 1935d, 1936a, 1936c). 

 Stronger concentrations produce irregular beating 

 and some times systolic arrest. 



y\/V\/lA/l/i/VWW\AAA/lA/ViAAAM/V 



Figure 231. — Effect of veratrine (cone. 1: 10,000) on 

 ventricular contractions of the isolated heart of C. 

 virginica. Temperature 20.5° C. Time interval, 5 sec. 

 Upper line — in sea water; lower line — immediately after 

 the perfusion with veratrine in sea water. 



CIRCULATORY SYSTEM AND BLOOD 

 "33-851 O— 64 17 



BLOOD VESSELS 



Lack of continuity between the arteries and 

 veins due to the presence of sinuses is the charac- 

 teristic featm'e of the open circulatory system of 

 bivalves. The spaces which function as capillaries 

 have no distinct walls, are of irregular shape, and 

 appear as slits in the tissue (fig. 79). Their pres- 

 ence imposes difficulty in the maintainance of 

 effective circulation of blood through the organs 

 and tissues. The deficiency is partially overcome 

 by the presence of pulsating vessels and accessory 

 hearts, which assist in the moving of blood through 

 the mantle. 



All blood vessels of the oyster have very thin 

 and delicate walls that are easily ruptured by a 

 slight increase in pressure. In anatomical prepa- 

 rations of the circulatory system, it is, therefore, 

 difficult to obtain complete penetration of arterial 

 and venous sj^stems by injection. Partial success 

 may be obtained by using a warm gelatine solu- 

 tion stained with appropriate dyes; by injecting 

 borax or lithium carmine and immediately placing 

 the preparation into 95 percent alcohol in which 

 the stain is precipitated; or by injecting vinyl 

 resin solution diluted with acetone (Eble, 1958). 

 For more detailed study the preparation may be 

 dehydrated and clarified in oil of cloves or in 

 cedarwood oil. Very small vessels may be in- 

 jected through a capillary tubing using aquaeous 

 solution of methylene blue, toluidin blue, or some 

 other suitable d.ye. Although no permanent prep- 

 aration can be obtained in this way, the method 

 is useful for tracing the connection between the 

 small vessels. 



Because the injection of the venous system is 

 even more difficult tlian that of the arteries, 

 knowledge of venous circulation in bivalves is 

 less complete than that of the arterial system. 

 Attempts to observe the movement of blood in- 

 side the veins usually are not successful because 

 the tissues are either too contractible or contain 

 so much glycogen that the vessels are obscured. 

 The description of the principal blood vessels of 

 the oyster given below is based on the examina- 

 tion of many specimens injected by various 

 methods and studied under a low power of 

 magnification. 



THE ARTERIAL SYSTEM 



The arteries can be recognized in microscopic 

 preparations by their well-developed walls lined 

 with a single layer of flattened endothelial cells 



253 



