34 THE MICROSCOPE. 



had specimens of these oysters examined under the microscope by 

 Prof. H. J. Rice, of this city, with the following result: 



He found that the digestive organs of the oysters were filled 

 with minute fragments of marine plants, or algae. The presence of 

 this substance gave the mouth or beard of the oyster a greenish hue. 

 The body of the bivalve was of a natural color. It has been feared 

 that this peculiar appearance was due to the contact of. the oyster 

 with copper in some form, but the experiment showed that this 

 could not be the case. In Europe green oysters are very common, 

 and careful experiments have been made there by Professor Sullivan 

 to discover the cause. He analyzed the mud from which they were 

 taken, but did not find any indications of the presence of a metallic 

 substance. He then placed some oysters in a solution of copper 

 and found that they readily assimilated it. Its presence was defected 

 by the body assuming a bluish-green appearance, while the beard re- 

 mained of its natural color. When the oysters were fed on algae, 

 the beards gradually turned green without the rest of the body be- 

 ing affected. 



On being provided with their natural food, which principally 

 consists of microscopical organisms known as diatoms, the mantle 

 returned to its ordinary color. 



Mr. Blackford states that he had noticed the same thing in 

 oysters coming from Virginia, and also that some taken from the 

 vicinity of Staten Island were likewise affected, but that it was prin- 

 cipally confined to the Shrewsburies. 



The greenish tint has caused much prejudice against such oysters, 

 but there does not seem to exist the slightest ground for it. The 

 green gill is not, according to the expert's report, the symptom of any 

 disease; in fact, oysters seem to thrive that feed on algae, which pro- 

 duces the objectionable color. 



Mr. Blackford has made arrangements with Prof. Rice to ex- 

 amine daily the fish received at the Fulton Market, in this city, 

 for the period of one year from the first of next June, and we look 

 forward to some important discoveries as the outcome of these in- 

 vestigations. In the examinations the viscera of the fish will be re- 

 moved and carefully dissected; the size, weight, time, and 

 place of capture will also be noted. The mint and roe 

 will be removed as well as the contents of the stomach, all of 



