SEA MUSSEL MYTILUS EDULIS. 



225 



the mussel in fuel value, but even this occupies a lower rank. The general excellence 

 of the mussel is due chiefly to the fact that there is little waste in the animal as a whole. 

 It is in the same class with the long clam, where the amount of edible material supplied 

 exceeds 50 per cent. The oyster, on the other hand, is at its greatest disadvantage in 

 this respect, for its heavy shell makes the percentage of refuse amount to more than 

 81 per cent. 



Table 6. — Comparative Composition and Fuel Value of Certain Shellfish. 1 



1 Data from Langworthy (1905). 



The relative value of food substances from the standpoint of economy can not be 

 determined from their chemical composition alone. It is necessary to know the actual 

 cost of the food principles supplied and the proportion which the body is able to metabo- 

 lize. 



In regard to the palatability of the sea mussel little need be said aside from the fact 

 that the flesh is tender and of fine quality and the flavor is superior to clams and equal to 

 that of the oyster. This statement is based on the testimony of a hundred or more per- 

 sons who reported on the comparative merits of these shellfish. 



Metabolism experiments made by Dr. D. D. Van Slyke, assisted by Dr. W. M. 

 Clark and Dr. C. B. Bennett, and reported in Field (191 1) demonstrated that the rate of 

 digestion and proportion of nutrients supplied to the body approximate very nearly those 

 of steamed beef, which is considered very digestible. It is unfortunate that we have no 

 similar data for the clam, oyster, and lobster flesh. 



The above evidence, however, is sufficient for drawing the conclusion that the sea 

 mussel is not only as palatable as the oyster, but is now the cheapest and most nutritious 

 shellfish which can be placed on the market. 



SEASONAL CHANGES IN STRUCTURE AND FOOD VALUE. 



Mussels, like oysters, undergo a series of structural and physiological changes during 

 the year which render them prime for market during one season and of very poor quality 

 in another. These changes are caused primarily by the reproductive activities of the 

 animal and secondarily by the rhythmic changes in the amount of food organisms present 

 in the water. 



It has been shown that by far the greater part of the mussel's body is devoted to the 

 production of genital products. Just before the spawning season the mantle and meso- 

 soma are greatly distended with reproductive tissue. It also covers the pericardium 

 and often envelops completely the outer walls of the liver. When in this state the shell- 

 fish are of maximum nutritive value, most palatable, and most attractive in appearance. 



