M. MATERIA MEDIC A, THERAPEUTICS, AND HYGIENE. 541 



one half of such dust consisted of organic matter, this being 

 the case from whatever place it was taken. He details the 

 result of experiments in regard to the power of this dust as a 

 ferment, the process being based upon the reduction of the ni- 

 trate of any base to a nitrite, in the presence of substances un- 

 der<>'oin2 fermentation. Due precautions were taken against 

 error in every instance, and it was found that dust possessed 

 the power of an active ferment ; and, furthermore, that the 

 dust taken from a great height, as that from Nelson's Pillar, 

 appeared to have as great or greater activity than that from 

 a building quite crowded to suifocation, this being due, prob- 

 ably, to the extreme lightness of the spores, almost approach- 

 ing to volatility. 1 A,October 21, 197. 



tyndall's eespieatoes. 



Professor Tyndall, in continuation of valuable applications 

 of the highest principles of science to questions of practical 

 moment bearing upon health and domestic economy, has late- 

 ly given a lecture before the Royal Institution upon the influ- 

 ence of dust and smoke. In this he renewed the suggestions 

 already made by him on a previous occasion as to the value 

 of the so-called respirators in excluding dust and other nox- 

 ious substances from the lungs. Such a respirator, in its sim- 

 plest form, consists of a small wad of raw cotton, which is 

 either to be taken into the mouth or bound over it. By this 

 simple application exhalations and emanations produced in 

 many branches of labor, such as grinding metals, spinning, 

 winnowing grain, etc., and including smoke and certain gases, 

 may be almost entirely arrested and rendered harmless. If 

 the cotton be moistened with a little glycerine, its serviceable 

 properties are materially increased so much so that it is pos- 

 sible to remain in quite dense smoke for a number of minutes 

 without inconvenience. 



Respirators of a more complicated character were suggest- 

 ed by Professor Tyndall in his lecture, to consist of a vessel 

 containing layers of cotton, charcoal, and slacked lime, pro- 

 vided with an aperture for the mouth, and so arranged that 

 the air can be first drawn through the apparatus, and then 

 discharged from the lungs by a side aperture, and without 

 passing again through the packing. In this way he obviates 

 the evil of having the cotton, etc., saturated with the moist- 



