50 
BULLETIN OF THE NATURAL HISTORY SOCIETY. 
Economics, Of all invertebrate animals that live in the' 
sea, perhaps of all invertebrate animals whatever, the Oyster 
is far the best known. It is very widely distributed, occurring, 
in nearly all the seas of the globe, and there are some seventy 
species recognized. How far back dates its use by man we cannot 
say, but the shells are found in very ancient kitchen-middens 
or refuse heaps in America, and still more ancient ones in 
Europe, This rather throws doubt upon the story sometimes 
•told that their excellence was first made known by an inquisi- 
tive walker on the seashore whose finger was pinched by one 
and carried for relief to his mouth. Toe historical accuracy 
of this tale is still further impugned by the fact that the same- 
is told of the origin of several other excellent edibles. 
That the Oyster is a nutritious and otherwise good article 
of food, all physicians, chemists and human experience agree. 
A discussion of its value compared with other food substances- 
will be found in the introductory part of this paper (p. 9).. 
It must be remembered that those tables express merely the 
absolute nutritive value of the various substances, and give no 
indication of the relative digestibility and other differences- 
which give this Mollusc its chief value. 
Though persons are occasionally found (of whom the 
writer is one), who dislike Oysters, we have never heard of 
any cases of actual poisoning by them. It is sometimes 
thought that those which have the gills of a green color are 
injurious, but repeated chemical analysis and careful experi- 
ments have shown that they are quite harmless. The green 
color is due to a pigment absorbed from their food, which, in 
such cases, consists chiefly of a particular kind of Diatoms- 
By feeding them other food for a time, their white color 
returns, and vice versa , by feeding white Oysters on these 
Diatoms they turn green. Indeed the epicures of Europe 
esteem the green more highly than the white, and in France- 
there are beds in which they are carefully fed to make them 
green. 
The United States is the greatest Oyster-producing country 
in the world. According to the census of 188b, this fishery is* 
