245 



The coiislciiit passage of the itlanktoii-huk'H respiratory currents tlirough the 

 mantle ra\ity, the presence of riuanlities of plankton in the nill lamellae, the ciliated 

 branchial groove leading forward to the mouth, and the presence of at least rudimentary 

 labial pal])s all indicate a partial utilization of plankton as food. The teredo which is 

 boring, and consequenth' growing to fill the larger cavity, recjuires proteins to provide 

 for growth and repair, and carbohydrates to turnish the energ\- reciuired for the boring 

 operation. This energy could indeed be su])plied from the protein material of the 

 plankton, but much more efficientU' by carbohydrates, inasmuch as these last are 

 completely oxidized and there is therefore no necessity of getting rid of nitrogenous 

 products. If, then, when its boring acti\ities are greatest, the teredo has a\'ailable a 

 considerable supply of carbohydrate material to furnish the necessary energy, and 

 that a^•ailable in proportion to the amount of work being done, it appears to be a 

 natural arrangement, admirably adapted to its needs. The carbohydrates of the wood 

 therefore play an important part in sup|il\ing the teredo with energ\- when it is most 

 needed. 



If the contlusion be accepted that the wood is partly digested and absorbed as 

 food by Teredo, some light is thrown ujjon the probable mechanism by which toxic 

 substances injected into the timbers of marine structures protect against teredo 

 attack. If partial digestion of wood occurs, it is clear that all substances contained in 

 the wood must be subjected to an intimate contact with the animal's digestive fluids 

 over a considerable period of time. Optimum conditions then prex'ail for the absorp- 

 tion of toxic substances, and their effectiveness is limited only by such factors as lack 

 of solubility, inability of their solutions to penetrate the walls of the digestive tract, 

 etc., these factors Ijeing dependent upon the properties of the agent and not on the 

 conditions of exposure. No case of failure of a given toxin can be ascribed tf) physical 

 isolation of the borings as we might expect if the wood were regarded as wholly un- 

 digested and merely mechanically handled by the teredo. 



These considerations offer practical suggestions in regard to (1) the commercial 

 preservative treatment of marine timbers, and (2) the testing of the toxicity of sup- 

 posed preservative substances. We may conclude that the established practice of 

 preserving marine timbers by impregnating the wood with toxic substances is a 

 rational and efficient process for introducing these substances into the animal's sys- 

 tem, for it is clear that the teredo cannot bore into the wood without being exposed 

 to the action of any toxins that are capable of entering its system through the digestive 

 tract. As to methods of carrying out toxicity tests, it would appear that those methods 

 which use the wood as a vehicle ff)r carrying the toxin possess a distinct advantage 

 over methods in which the toxin is introduced into the animal by some other means. 



The practice followed by this Committee of testing various preservatives by 

 immersing in the Bay for considerable periods of time samples of timber treated with 

 the preservatives in question accordingly affords a much better basis for sound con- 

 clusions as to the usefulness of these treatments than would the alternative of direct 

 toxicity experiments in the laboratory. 



