The average composition of the principal fish, crustacea, etc., used for food is shown in the table below. That of others less frequently eaten is similar.
Fish usually contains less fat than is found in meat. There is, however, much difference in the fat content of the various kinds of fish. They may, indeed, be roughly divided into throe classes: The first class would include those con taining over 5 ix-r cent. fat; the second those containing between 2 and 5 per cent.; and the third those containing less than 2 per cent. The first group would include such fish as salmon. herring, Spanish mackerel, and butter-fish: the second. whitefish. mackerel. mullet, halibut, and porgy; the third, smelt, black bass, blue fish, white perch. weakfish, brook-trout., hake, flounder. yellow perch. pike, pickerel. sea-bass, cod, and haddock.
When judged by its composition, the place cf fish in the diet is the same as that of meat; that is, it is supplementary to cereals and other vege tables, most of which, as wheat, rye, maize, rice, potatoes, etc., are rich in carbohydrates, which are not present in appreciable amounts in the flesh of fish. Preserved fish, as a rule, show a small percentage of refuse, with the exception of a few kinds which are preserved whole. The percentage of actual nutrients is much larger than in the corresponding fresh fish,•owing to the removal of a large part of the refuse and more or less water. The gain in nutrients is mostly represented by protein. which is the most valu able nutrient. Canned fish, which is in effect cooked fish, compares favorably as regards com position with the fresh material. Generally speaking, the amount of refuse is small, since the portions commonly rejected in preparation for the table have been removed before canning. Shellfish resemble meat and food fishes in general composition. They contain, however, an appre ciable amount of carbohydrates. Judging by the relative amount consumed, oysters are the most important of the shellfish. Speaking roughly, a quart of oysters contains on an average about the same quantity of actual nutritive substances as a quart of milk, or three-fourths of a pound of beef, or two pounds of fresh codfish, or a pound of bread.
A number of experiments have been made with man to learn how thoroughly fish is digested and to compare it in this respect with other foods. It has been found that fish and lean beef are about equally digestible. In each case about 95 per cent, of the total dry matter, 97 per cent. of the protein, and about 95 per cent. of the fat were retained by the body. Other experiments of
the same character indicate that salt fish is less thoroughly digested than fresh fish. The nutri tive value of shellfish, as of other fish. depends to a considerable extent upon their digestibility; but so little is known upon this point that nothing more can be said with certainty here than that oysters belong to the more easily digestible class of foods. So far as can be learned no experiments have been made which show how thoroughly crabs, clams, and other crnstacea, turtle and terrapin, and frogs' legs are digested. Inspection of a considerable number of dietary studies of families of farmers. mechanics, profes sional men, and others, carried on in different regions of the United States, shows that out of the 20 per cent. of the total food and the 43 per cent. of the total protein obtained from animal sources, only about 2 per cent. of the total food and 4 per cent. of the total protein is furnished by fish, shellfish, etc., showing to what a limited extent this valuable food is used in the average household. it is not improbable that in communities where fishing constitutes the principal industry much larger quantities are consumed. It has been found that the laborers employed in the fisheries of Russia Consume from 26 to 6 of fish daily. This, with some bread, millet mal, and tea, constitutes their diet throughout the fishing season. These quantities are unusually large, but no had effects are men tioned as following the diet.
There is a widespread notion that fish con tains large proportions of phosphorus, and on that account is particularly valuable as brain food. The percentages of phosphorus in speci mens thus far analyzed are not larger than are found in the flesh of other animals used for food. But even so. there is no experimental evidence to warrant the assumption that fish is more valuable than meats or other food material for the nourishment of the brain. The opinion of eminent physiologists is that phosphorus is no more essential to the brain than nitrogen, potas sium, or any other element which occurs in its tissues. The value commonly attributed to the phosphorus is based on a popular misconception of statements by one of the early writers on such topics. It should be stated that most physiolo gists regard fish as a particularly desirable food for persons of sedentary habits, since it is easily digested and not too hearty. While, so far as can be learned, such statements do not depend upon experimental evidence, they are thought to embody the result of experience.