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Page:Popular Science Monthly Volume 29.djvu/262

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point of impact is precise, and the body glances from the rock. The collision is so accurately gauged that no harm is done. And similarly, and with a great variety of ingenious posturing, the fish subjects all parts of its body to this treatment. It even contrives to scratch the top of its head, by bringing the desired spot into the proper position at the precise moment of the glancing impact with the stone. The feat is delicate and deftly, as if an acrobat should in his somersaults comb his hair against a rock with no harm done every time.

Having enjoyed the use of a large aquarium for the study of fishes, it has been an object with me to anticipate their wants. Hence I have purposely given them scratching-stones properly adapted to their needs. I was surprised that a favorite object for this purpose was a large live river-mussel, the Anodonta excurvata. The corrugations of the shell, which mark its growth, form a series of smooth ridges, upon and against which, with their contortions of twists and bends and tilts, these fishes glance in scratching themselves. As to ichthyic emotion, one can not say much. That they enjoy these exercises, I am sure; and I almost think they know their benefactor, for they come at his call at feeding-time—though up to this present writing I have not observed anything that might be interpreted as a grateful recognition of benefits conferred; certainly nothing commensurate with the canny benediction, "God bless the Duke of Argyll!"



IT is a well-known fact that food undergoing decomposition—spoiling, as it is termed—is unwholesome. Cases of poisoning that have occurred on the partaking of meat, fish, sausage, and cheese, that is, food of animal origin, will be readily recalled, for on such occasions the daily press has rarely failed to sound notes of warning. Until quite recently, however, the nature of these poisons was veiled obscurity, and it is chiefly owing to the excellent investigations of Professor L. Brieger, at Berlin, that some light has been thrown on this subject.

As the study of the poisons of putrefaction is not only of great interest from the scientific point of view, but of the utmost importance in everyday life (for these poisons may be generated and produced daily in pantry and cellar), it seems desirable, in the interest of hygiene, to relate the new discoveries that have been made in this field, and review the earlier work done in it.

Schlossberger, who for some time past has been compiling statistics of cases of poisoning caused by food that had spoiled, records for Swabia alone, from the year 1793 to 1853, four hundred cases of sick-