MOLLUSCA. 43 
removal necessary, as has repeatedly happened in 
the dockyard of Plymouth. To preserve the tim- 
bers used there, and exposed to them, the plan now 
adopted is to cover the parts under water with 
short broad-headed nails, which, in salt water, soon 
invests the whole with a strong coating of rust im- 
penetrable by their augers. ‘The plan appears to 
have proved effectual, for, in the harbours of Ply- 
mouth and Falmouth, where the Teredo was once 
abundant, it is now rare or not to be found; but 
in other parts it has still a residence, and within 
these few years it has materially injured or de- 
stroyed many of the piles used in the construction 
of the pier at Port Patrick, on the coast of 
Ayrshire; and the Limnoria terebrans, a crus- 
taceous insect, co-operating with it, the result 
of their united efforts can hardly fail to be the 
utter and speedy destruction of all the timber in 
ihe pier.’ * 
Another kind of injury is dependent on the fact 
that certain species, which are generally eatable 
and even wholesome, become at certain times highly 
poisonous. Some foreign species are liable to this 
fatality, particularly oysters, both in the East and 
West Indies. But we need not go to distant coun- 
tries for cases in point. The Mussels of our own 
rocks, though generally sold and eaten by many 
persons without fear, are well known to be fickle in 
their qualities, and many cases are on record in 
which their use has proved fatal. One of these, 
well authenticated, and investigated by scientific 
medical men, occurred at Leith in June 1827. Many 
of the poor of this town were poisoned by eating 
mussels which had been collected in the docks. 
* Tntroduction to Conchology, p. 11. 
