P OP ULAR MIS CELL ANY. 



285 



es. Again, a definition of poisons has been 

 based on the faet that while certain articles 

 of food undergo decomposition in the stom- 

 ach, poisons do not. Then water is a poi- 

 son, 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 bod- 

 ies, viz., "germs" which, when absorbed by 

 an animal, bring on such diseases as rabies, 

 small-pox, cholera, etc. in short, the zy- 

 motic diseases ; and, in the second place, 

 the true poisons, such as arsenic, strychnine, 

 aconitine, etc. These latter substances are 

 well-defined chemical individuals. When in- 

 troduced 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 character- 

 istic feature is that their noxious power may 

 be decreased or even extinguished by dilu- 

 tion. 



The other class, however, the ferments, 

 are not definite chemical principles, capable 

 of being isolated, of entering into combina- 

 tion with other bodies, and of being sepa- 

 rated 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 oth- 

 ers is remarkable. This difference of sus- 

 ceptibility often exists between individuals 

 of the same species, being developed in some 

 cases by natural selection, in others by ha- 

 bituation. The author of the paper in the 

 " Journal of Science " gives the following 

 list of caterpillars which feed on poisonous 

 plants : Gonopteri/x rhamni, on JRhamnus 

 catharticut, ; Thats polyxcna, on species of 

 Aristolochia ; Danais archippus and chrysip- 

 pics, upon various Asclepiads ; Dcihphila 

 galii, Nicea, and Euphorbia, on specie8 of 

 Euphorbia ; Chcerocampa nerii, on the ole- 

 ander ; Sphinx polia cappa, on staves-acre ; 

 Heliothisa armigera, on tobacco ; and Chrys- 

 optera mohcta, 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 English- 

 man, Wentworth L. Scott. The pen con- 



sists 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 cop- 

 per 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 

 Rub mkorff coil. The other pole is connect- 

 ed 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 per- 

 forations, like those produced by Edison's 

 electric pen. The instrument is as light as 

 a common pen. The cost of the whole ap- 

 paratus is trifling, about eighteen francs. 



Alnm as an Adulterant of Baking-Pow- 

 ders. 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 bak- 

 ing-powders examined by him were grossly 

 adulterated. Dr. Mott found that the inju- 

 rious powders are composed of alum and bi- 

 carbonate 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 pre- 

 vent decomposition. The injurious effects 

 of alum on the digestive organs have been 

 pointed out by eminent chemists and physi- 

 cians : it produces dyspepsia, constipation, 

 vomiting, griping ; it is a powerful astrin- 

 gent, acting chemically on the tissues. Says 

 Dumas, the French chemist : " It is to be 

 feared that this salt (alum) exerts a dead- 

 ly action by its daily introduction into the 



