PREFACE V 



reader regarding the extent to which different reports have shed 

 hght on related mechanisms. 



The primary purpose of the symposium was to examine the con- 

 ditions in which mineraUzed structures — inchiding rocks, corals, 

 shells, antlers, bone, ivorv, cementum, dentin, and enamel — are 

 subject to destruction by various marine and subterranean organisms 

 such as boring sponges, mollusks, snails, octopuses, worms, algae, 

 and fungi, as well as by the action of the giant cells tvpical of 

 lacunar resorption and the oral bacteria responsible for tooth decay. 

 Beyond the morphological and cellular levels of observation, the 

 symposium also served to delineate present knowledge and various 

 areas of ignorance regarding specific chemical agents which lead to 

 the disruption and dissolution of the inorganic salts and organic 

 matrices of mineralized structures; e.g., glandular secretions and 

 various extracellular and intracellular metabolites, acids, chelators, 

 enzymes, and combinations of chemical and physical factors. 



When comparing the various mineralized structures that succumb 

 to decalcification in biological systems, one is impressed by the 

 broad spectrum of their chemical and physical properties, as well 

 as bv the varietv of the biological organisms and biochemical agents 

 involved in their dissolution. Rock-boring organisms can disintegrate 

 not onlv relatively soft sedimentary rock, but also densely mineral- 

 ized calcareous products. Boring sponges burrow not only into 

 corals, but also into limestone and shells whether composed of cal- 

 cite or of aragonite. Gastropods "drill" into the shells of bivalves as 

 well as those of their own fellow snails. Excised gastropod boring 

 organs can act on hard tissues other than shells and will produce 

 etchings when the calcium phosphate crystals of human enamel and 

 dentin are exposed to them in vitro. Indigenous oral microorganisms 

 evidently are endowed with a dual capacity to produce agents which 

 can dissolve and digest hard tissues of as contrasting composition 

 as enamel and dentin, so as to cause tooth decay, now definitely 

 established as being of bacterial origin. Subterranean fungi under 

 postmortem conditions produce boring canals by a dissolution of 

 the collagen and calcium phosphate in buried bone, ivory, cemen- 

 tum, and dentin, but leave dental enamel alone. Marine fungi at- 

 tack the shells of bivalves (calcite) and snails (aragonite) and 



