BULLETIN OF THE UNITED STATES FISH COMMISSION. 188 



The only organic pathological changes which the writer has hitherto 

 observed to accompany this discoloration, as one of its effects, is the 

 lodgment of the tinged blood corpuscles in the depressions between 

 rlie muscular trabecular of the cardiac walls. Sometimes these cor- 

 puscles, thus arrested in the ventricular chamber of the heart, form ;i 

 thick adherent coating over the inside of the ventricle. The arrest of 

 corpuscles, and their accumulation in cysts developed in the vicinity of 

 vessels iu the mantle, also occur, but this condition seems to be a rare 

 one. When freed from the cavities in which they have been arrested, 

 these blood corpuscles are very easily dissociated, if the, animal has 

 been previously hardened in alcohol or chromic acid. Microscopic 

 examination shows them to be blood corpuscles, which belong to the 

 animal in which they are found, and not foreign parasitic bodies of a 

 vegetable nature, as is proved by their size, structure, and non-posses- 

 sion of cellulose walls. 



What has been said above relative to the source and nature of the 

 discoloriug pigment abnormally present in the tissues of the oyster as 

 a diffusable substance applies also to the substance which has discol- 

 ored the gills and palps of the specimens of clams sent from Stonington, 

 Conn. During the last three years the writer has frequently been told 

 by fishermen and oystermeu, at different localities along the eastern 

 coast, that the flesh of clams was sometimes discolored much in the same 

 manner as that of oysters; but until recently no opportunity has pre- 

 sented itself to study this condition in the clam. Skeptical at first, the 

 Stonington specimens demonstrated very clearly to the writer that the 

 nature and source of the discoloriug pigment are very similar, if not 

 identical, in the cases of both the oyster and the clam. 



The researches which have been made upon the Stonington specimens 

 were conducted as follows : A pipette was thrust into the mouth and 

 stomach, to get some of the food materials ; some of the contents of 

 the rectum of several individuals was also examined. The result was 

 that very little could be determined as to what had been the food of the 

 animals, except that diatoms- had been consumed in moderate quan- 

 tity. There was no great abundance of empty diatom frustules, such 

 as is sometimes observed in the oyster. These diatoms were all navic- 

 ular in form, but belonged to several different species, so that it was 

 impossible, with the material at hand, to find out which one had supplied 

 the coloring matter, because the soft material had been dissolved out 

 of the frustules entirely, leaving them colorless and empty. Other de- 

 bris among the contents of the rectum showed that fragments of small 

 arthropods had been swallowed. 



The investigation' of the soft parts which had been discolored was 

 more satisfactory, because in these cases the method of microtomy was 

 applicable. But before entering upon a discussion of this aspect of the 

 investigation it may be well to describe the condition in which the 

 specimens reached the writer, and in what way they were affected. 



