es. Again, a definition of poisons has been based on the fact that while certain articles of food undergo decomposition in the stomach, poisons do not. Then water is a poison, for it does not suffer decomposition in the system.
But, turning aside from these definitions, we find included under the general name of "poisons" two very different classes of bodies, viz., "germs" which, when absorbed by an animal, bring on such diseases as rabies, small-pox, cholera, etc.—in short, the zymotic diseases; and, in the second place, the true poisons, such as arsenic, strychnine, aconitine, etc. These latter substances are well-defined chemical individuals. When introduced into the system they set up morbid action almost immediately, and if the dose be sufficient the symptoms go on increasing in violence till death ensues. A characteristic feature is that their noxious power may be decreased or even extinguished by dilution.
The other class, however, the ferments, are not definite chemical principles, capable of being isolated, of entering into combination with other bodies, and of being separated again; they are, so far as we know, living organisms of low type.
The immunity of certain animals from the action of poisons which are fatal to others is remarkable. This difference of susceptibility often exists between individuals of the same species, being developed in some cases by natural selection, in others by habituation. The author of the paper in the "Journal of Science" gives the following list of caterpillars which feed on poisonous plants: Gonopteriyx rhamni, on Rhamnus catharticus; Thats polyxena, on species of Aristolochia; Danais archippus and chrysippus, upon various Asclepiads; Deihphila galii, Nicea, and Euphorbiæ, on species of Euphorbia; Chærocampa nerii, on the oleander; Sphinx polia cappa, on staves-acre; Heliothisa armigera, on tobacco; and Chrysoptera moneta, on monk's-hood.
A New Electric Pen.—In the "Monde de la Science" is a description of an improved electric pen, much cheaper than Edison's, and not so fatiguing to the operator; the inventor would appear to be an Englishman, Wentworth L. Scott. The pen consists of an open glass tube drawn out to a point at one end, where there is a minute orifice. Within the tube is a copper wire, to which a fine platinum point is soldered toward the lower end of the pen. This copper wire is held in the middle of the tube by means of a cork stopper at the larger end (the upper end of the pen). The point of platinum should just reach the tip of the pen. To work the instrument the copper wire is connected with one of the poles of a Ruhmkorff coil. The other pole is connected with a zinc plate, on which the paper is to be laid. The circuit is now closed, and so soon as the current flows it causes the interrupter of the Ruhmkorff coil to vibrate. The pen is then made to move over the paper, as in writing, care being taken only to touch the glass tube, for fear of electric shocks, and electric sparks are seen to pass with great rapidity between the point of the pen and the paper. On holding up the paper between the eye and the light, the track of the pen is seen to consist of minute perforations, like those produced by Edison's electric pen. The instrument is as light as a common pen. The cost of the whole apparatus is trifling, about eighteen francs.
Alum as an Adulterant of Baking-Powders.—Dr. Henry A. Mott, Jr., employed as chemist for the Indian Department, having made analyses of different baking-powders, publishes in the "Scientific American" as the result of his investigations the statement that at least fifty per cent, of the many baking-powders examined by him were grossly adulterated. Dr. Mott found that the injurious powders are composed of alum and bicarbonate of soda, oftentimes containing also terra alba, insoluble phosphate of lime, etc. The best powders are composed of bitartrate of potash (cream of tartar), tartaric acid, carbonate of ammonia, and bicarbonate of soda, held together by a little starch to prevent decomposition. The injurious effects of alum on the digestive organs have been pointed out by eminent chemists and physicians: it produces dyspepsia, constipation, vomiting, griping; it is a powerful astringent, acting chemically on the tissues. Says Dumas, the French chemist: "It is to be feared that this salt (alum) exerts a deadly action by its daily introduction into the
