There is one respect in which acetylene and other flame illuminants are superior to electric lighting, viz., that they sterilise a larger volume of air. All the air which is needed to support combustion, as well as the excess of air which actually passes through the burner tube and flame in incandescent burners, is obviously sterilised; but so also is the much larger volume of air which, by virtue of the up-current due to the heat of the flame, is brought into anything like close proximity with the light. The electric glow-lamp, and the most popular and economical modern enclosed electric arc-lamp, sterilise only the much smaller volume of air which is brought into direct contact with their glass bulbs. Moreover, when large numbers of persons are congregated in insufficiently ventilated buildings--and many public rooms are insufficiently ventilated--the air becomes nauseous to inspire and positively detrimental to the health of delicate people, by reason of the human effluvia which arise from soiled raiment and uncleansed or unhealthy bodies, long before the proportion of carbonic acid by itself is high enough to be objectionable. Thus a certain proportion of carbonic acid coming from human lungs and skin is more harmful than the same proportion of carbonic acid derived from the combustion of gas or oil. Hence acetylene and flame illuminants generally have the valuable hygienic advantages over electric lighting, not only of killing a far larger number of the micro-organisms that may be present in the air, but, by virtue of their naked flames, of burning up and destroying a considerable quantity of the aforesaid odoriferous matter, thus relieving the nose and materially assisting in the prevention of that lassitude and anæmia occasionally follow the constant inspiration of air rendered foul by human exhalations.