Acute tolerance, or tachyphylaxis, is a phenomenon in which successive equal 

 doses of a pharmacologic agent cause diminished responses when administered at 

 frequent intervals. Experiments on isolated hard clam hearts showed that 

 tachyphylaxis induced by levarterenol was blocked most effectively by 1- 

 ephedrine, intermediately by dZ-ephedrine , and least by d-ephedrine . 

 Levarterenol and epinephrine appear to act at the same receptor site; thus it 

 is suggested that ephedrine could block levarterenol responses by acting on the 

 same receptor sites. Positive intropic responses at higher doses of ephedrine 

 isomers showed that both agents may act at the same site. Ephedrine may block 

 inhibitory cardiac sites on which levarterenol acts, thus allowing 

 levarterenol to stimulate. - J.L.M. 



350 



Clark, George R. , II. 1968. 



Mollusk shell: daily growth lines. Science 161(3843): 800-802. 



Ridges forming the concentric sculpture on shells of laboratory grown Pecten 

 diegensis show daily periodicity. Missing growth lines account for all 

 scatter in the data, so the maximum, not the average, line count is most 

 representative. - J.L.M. 



351 



Clark, George R. , II. 1974. 



Growth lines in invertebrate skeletons. Ann. Rev. Earth Planetary Sci . , 2 

 Ann. Reviews, Inc., Palo Alto, Calif., p. 77-99. 



This review paper cites several references to Mercenaria mercenaria abstracted 

 elsewhere in this bibliography. It reviews growth lines as records of the 

 environment, and practical applications of growth line records. Included is 

 a summary of periodic events, such as tides, temp variations, spawning, and 

 influence of declination and latitude of sun and moon on environmental 

 variables. - J.L.M. 



352 



Clark, John R. 1969 . 



Thermal pollution and aquatic life. Sci. Am. 220(3): 18-27. 



Effects of rising temp on spawning of oysters and clams (species not 

 identified) is particularly dramatic. They spawn within a few hours after 

 water temp rises to the critical level. - J.L.M. and M.W.S. 



353 



Clark, J. R. 1970. 



Living resources. In Proc. Symp. Water Poll. Greater N.Y. Area. Gordon 

 & Breach, N.Y., p. 101-106. 



354 



Clarke, Arthur H. 1971. 



Littorina littorea, native or introduced? The Biologist 53(3): 160-162. 



It seems likely that by the 17th and 18th centuries a warm- stenothermal 

 physiological race of L._ littorea was distributed in a way similar to that 

 of other warm-stenothermal species, like Mercenaria mercenaria, among 

 others, in eastern Canada, in the vicinity of Northumberland Strait and a 

 few semi-enclosed bays along the Nova Scotia coast. - J.L.M. 



355 



Clarke, John R. 1978. 



The response of an intertidal bivalve heart to hypo-osmotic and ionic 

 stress at high pressure. Comp. Biochem. Physiol. 61A(1): 35-42. 



Research was done on Modiolus demissus . Mercenaria mercenaria is not 

 mentioned. - J.L.M. 



98 



