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X.— EXPERIMENTS IN FEEDING WITH METALLIC SALTS. 
With the object of tr} ing to produce in the laboratory results similar to those 
observed in Nature, and with the view of testing the part which the absorption of 
metallic salts might play in colouring the oyster, and in possibly rendering it unfit for 
human food, we have made, during the last couple of years, a large number of experi- 
ments by keeping oysters in tanks in which definite quantities of various salts of iron 
and copper had been added to the sea-water.* 
In all cases we first of all ascertained that our oysters, both x'\mericans and 
Natives, were health)' and colourless, so far as we could judge by observing them 
through the opening between the shells when in the expanded condition. We could 
make sure at any rate that the mantle and the gills were not green, and we always 
opened a few specimens of the same batch as a control. 
In the first place, we tried the effect of pieces of copjjer, copper filings, and 
copper dust lying in the bottom of the aquarium ; and similarly, of steel filings, old 
rusty nails, and other fragments of iron. We also kept oysters for some time in an 
old copjjer vessel, and along with copper pyrites and other ores of copper. None of 
these gave any definite result. 
We then, w ith Dr. Kohn's assistance, tried measured quantities and strengths of 
various metallic salts. On Feh. 5th, 1896, we added 0.2 per cent, of sulphate of copper 
to 10 litres of sea-water in which a few oysters were placed ; while another set of 
oysters had the same quantity of ferric ammonium citrate added to their 10 litres of 
water. From these we got no definite results. The oysters lived better in the iron water 
than in the copper. The only staining was a deposition on the shell and in the mucus 
of the mantle edge, and some post-mortem colouration in the case of those that died. 
On Feb. 27th we started three colourless American oysters in each of three 
aquaria containing insoluble salts, viz., sulphide of iron, ferric hydrate, and copper oxide, 
in each case 50 grains being added to one gallon of sea-water. By March 5th, those 
in the copper oxide fluid were evidently sickly, while the others seemed healthy. On 
March 12th, those in the copper oxide no longer reacted under stimulation, and were 
evidently just dead. On being opened, they had all the appearance of ordinary yellow 
oysters, the gills and palps were normal, and there was no trace of staining in any 
part. On March 21st, one from each of the other aquaria was opened. They were 
* Recently Carazzi has stated that oysters fed with similar dilute iron solutions acquire a pale yellowish 
colour in certain parts (branchial epithelium and the cosophageal mucous membrane), and that in these parts micro- 
scopic tcbts show the [iresence of granules of iron. The actu il meaning of these results can hardly be recognised 
without comparative and quantitative data. 
