FOOD VALUE OF SEA MUSSEES. 
93 
the farmer who ignores the first principles of agriculture. Up to the present time, 
however, very little study has been made of the food of marine animals or of the relative 
fertility of the waters in various parts of the sea. Such investigations as those of Peck 
(1894 and 1896) on the sources of marine food, and of Moore (1907) on the food of the 
oyster are of very great economic value. 
My observations on the food of the mussel were necessarily limited. They were con- 
fined to the vicinity of Woods Hole and to the months of July and August. Lack of 
time did not permit a determination of the food value of the water over the mussel beds. 
During the summers of 1908 and 1909, however, a microscopic examination was made of 
the material found in the digestive tracts of 50 mussels. 
Two methods were employed. The first was to extract the stomach contents by 
means of a pipette, which was thrust down the animal’s gullet. The substance drawn 
out from the stomach was mixed with a few drops of water and a thin layer spread 
across the middle of a microscopic slide. The slide was then passed several times 
through the flame of an alcohol lamp, until the organisms were thoroughly fixed by the 
heat and the water almost evaporated to dryness. A drop of glycerin or of hot glycerin 
jelly was next applied and a cover glass pressed down upon it. Permanent mounts 
were later made from these preparations by cleaning the slides outside the boundary 
of the cover glass and ringing the mounts first with King’s cement and, twenty-four 
hours later, ringing them again with asphaltum. This method proved best for pre- 
serving the animal forms, Protozoa, found in the stomach. 
The second method was to place the mussels, immediately after removal from their 
natural beds, in small dishes of filtered sea water. After two or three hours’ time the 
bottoms of the dishes were covered with intestinal discharges, which were removed by 
means of a pipette and transferred to a vial containing 95 per cent alcohol. After the 
sediment had completely settled the alcohol was drawn off and fresh alcohol added. 
The process was repeated, using absolute alcohol instead of the weaker grade. This 
was followed by a few minutes’ treatment with xylol, and after removing most of the 
xylol three or four drops of a rather thin solution of Canada balsam were added. This 
mixture was allowed to stand for a few hours, until the xylol, sediment, and balsam were 
thoroughly mixed. Then, by means of a pipette, a large drop was transferred to a 
microscopic slide and on it was placed a cover glass. This method was found best for 
the preservation of the plant organisms which are known as diatoms. The diatoms, 
thus prepared, have had the pigments and coagulated protoplasm more or less com- 
pletely removed, leaving a clear view of the striations and other markings on the 
skeleton. 
The food of the mussel was found to consist of microscopic plants and animals which 
are carried by chance to the mollusk by water currents and are swept into the mouth 
by means of cilia on the gills and palps. The wall of the gullet is also lined with cilia, 
which direct the movement of the food material into the stomach. Not only food, but 
dirt and other indigestible substances are swept in. From the alimentary tracts of 50 
