250 THE POPULAR SCIENCE MONTHLY. 



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 

 ]3arts 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 ! " 







THE POISONS IX SPOILING FOOD. 



Bt JULIUS STDTDE. 



IT is a well-known fact that food undergoing decomposition spoil- 

 ing, 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 in ob- 

 scurity, and it is chiefly owing to the excellent investigations of Pro- 

 fessor 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 impor- 

 tance in every-day life (for these poisons may be generated and pro- 

 duced 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 statis- 

 tics 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- 



