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Page:Popular Science Monthly Volume 32.djvu/92

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82
THE POPULAR SCIENCE MONTHLY.

whole boat-load. The remainder were taken to the brackish water of a stream emptying into the bay and kept upon the floats for forty-eight hours, this being the usual practice in the floating of oysters in this region. At the end of that time, the oysters were taken from the floats, and a number fairly representing the whole were selected as before. Two lots, one floated and the other not floated, were thus taken from each of two different beds. The four lots were brought to our laboratory for analysis.

The specimens as received at the laboratory were weighed. Thereupon, the shell-contents were taken out, and the shells and shell-contents both weighed. The solid and liquid portions of the shell-contents—i. e., the flesh or "solids" and liquor or "liquids"—were weighed separately, and then analyzed. We thus had, for each lot, the weights of flesh and liquids which, together made the weight of the total shell contents, and the weight of the shells, which with that of the shell contents made the weight of the whole specimens. We also had, from the analyses, the percentages of water, nutritive ingredients, salts, etc., in the flesh and in the liquids. From these data the calculations were made of the changes which took place in floating. For the details, which are somewhat extended, I may refer to the publication mentioned above. It will suffice here to give only the main results. It is assumed that the changes in the composition of the body of the animal, due to respiration, nutrition, excretion, etc., during the floating would be too small to be taken into account.

The body of the animal may be regarded as made up of water and so-called water-free substance. The water-free substance contains the nutritive ingredients or "nutrients." These may be divided into four classes: 1. Protein compounds, the so-called "flesh-formers," which contain nitrogen[1]; 2. Fatty substances, classed as fats; 3. Carbohydrates; 4. Mineral salts. These constituents of the flesh of oysters have been but little studied. It is customary to assume them to be similar to the corresponding compounds of other food-materials, but very probably the difference, if known, might prove to be important. The mineral matters especially, which are very large in amount, appear to include considerable of the salts of sea-water. Of the nature of the ingredients of the liquids but little is known. They consist mainly of water and salts and the amounts of their ingredients which are commonly reckoned as protein, fats, and carbohydrates, are very small, so that whatever error there may be in classing them with the ordinary nutrients of food, it will not very seriously affect the estimates of nutritive values.

During the sojourn in brackish water, both the flesh (body) and the liquid portion of the shell-contents of the oysters suffered more or less alterations in composition. In order to show clearly what the principal changes, as shown by the chemical analyses, were, it may per-

  1. The protein is estimated in the usual way by multiplying the nitrogen by 6·25.