1812 



Towe, Kenneth M., and George R. Thompson. 1972. 



The structure of some bivalve shell carbonates prepared by ion-beam 

 thinning: A comparison study. Calcif. Tissue Res. 10(1): 38-48. 



In cross-polarized light from an ion-beam thinned sample, the boundaries 

 between prisms in Mercenaria mercenaria are well shown and growth lines 

 running normal to the prisms can be seen. In the electron microscope the 

 transmission images show that the prisms are not single crystals, as they 

 appear to be in polarized light, but are constructed of numerous smaller 

 crystalline units with their long axes parallel and subparallel to those 

 of the larger prisms. The polycrystalline nature of the prisms has been 

 confirmed by selected-area electron diffraction. - J.L.M. 



1813 



Tower, Donald B., and Donald McEachern. 1948. 



Experiences with the 'Venus' heart method for determining acetylcholine. 

 Canadian J. Research 26E(2): 183-187. 



Existing methods for determination of acetylcholine (ACh) were not satisfactory 

 because they lacked sensitivity to micro-amounts, the ACh molecule is unstable, 

 and ACh is similar chemically and pharmacologically to other constituents of 

 biological materials. Chemical analysis would not detect less than about 0.1 

 mg of pure substance. Sensitivity of Venus heart to ACh was reported 

 originally by Prosser and Prosser [1937) and studied further by others (all 

 abstracted elsewhere in this bibliography) . Adaptation of the method for 

 biological assay of ACh was described by Wait (1943) and Welsh (at that time 

 in press) . The method is described and illustrated. Isolated ventricle of 

 V. mercenaria is stable for many hours. Its minimal sensitivity for ACh was 

 between 0.005 and 0.01 ug %. The method is simple and highly specific and the 

 preparation may be used repeatedly, as often as every 5 to 10 min. The effect 

 of ACh on ventricular contractions is one of partial or complete inhibition of 

 systolic contraction without significant effect on rate. Extent of inhibition 

 is almost directly dependent on amount of ACh present. Isolated ventricle is 

 highly specific. It is insensitive to most other constituents of biological 

 tissues and fluids, particularly K, histamine, and adrenaline. It is not 

 susceptible to pH over at least the range pH 5 to 8.5. It is also insensitive 

 to anticholinesterases such as physostigmine (eserine) , prostigmine, and di- 

 isopropylf luorophosphate (DFP) . In active biological samples the identity of 

 ACh can be established through its destruction by alkali-heat hydrolysis. 

 Venus ventricle shows seasonal variations in responsiveness to ACh. Poor 

 preparations can be restored to normal by addition of ergot alkaloids to the 

 medium to give a final concentration of 1:1,000,000. - J.L.M. 



1814 



Townes, H. K., Jr. 1939. 



Ecological studies on the Long Island marine invertebrates of importance as 

 fish food or bait. State N.Y. Conserv. Dept. 28th Ann. Rept. 1938, 14 (Suppl.): 

 163-176. 



Venus mercenaria is common in rather shallow water on bottoms of gravel, sand or 

 mud. Commonest on sand. Often used as bait. - J.L.M. 



1815 



Tressler, Donald K. 1923. 



Marine Products of Commerce. Chapter 28 - The clam industry of the United 

 States. New York: 532-547. 



Revised edition, published in 1951 under names of Tressler and Lemon, is 

 abstracted below. - J.L.M. 



504 



