MEANS FOR KILLING BACTERIA. 669 



the action was at least eight hours. More recent 

 investigations by Koch and Wolffhiigel have however 

 shown that sulphurous acid, even when as concentrated 

 as possible a degree of concentration which cannot be 

 attained in practice only kills spores imperfectly ; even 

 with regard to non-spore-bearing bacteria the action is 

 uncertain when present in 10 per cent, by volume if the 

 layers to be disinfected are at all thick. Further, 

 sulphurous acid penetrates with considerable difficulty 

 into the deeper layers of masses of clothing, &c., and 

 only has a certain amount of disinfecting action when 

 the objects have been previously moistened, while at the 

 same time it causes considerable injury to them. 

 Dujardin-Beaumetz has recently again recommended 

 sulphurous acid, and asserts, as the result of practical 

 experience and of experiments with cultivations of 

 bacteria in infusions, that the burning of 20 grammes 

 of sulphur per cubic metre is sufficient for complete 

 disinfection. The experimental proofs brought forward 

 by Dujardin are, however, quite insufficient. 



Chlorine and bromine have, on the whole, a very Action of 

 marked action, more especially when the objects have bromine . an 

 been moistened, or when the air is saturated with 

 moisture. In dry air, and where the material is dry, 

 even several parts per 100 of these vapours in the air 

 do not cause complete disinfection. Where, however, 

 the materials have been previously artificially moistened 

 the presence of '3 per cent, by volume of chlorine and 

 '21 per cent, of bromine when acting for three hours is 

 sufficient to kill all spores ; *03 to *04 per cent, by volume 

 also suffices when it acts for twenty-four hours. This 

 favourable effect has, however, only been obtained in 

 experiments in laboratories, and not where the experi- 

 ments were carried on on a larger scale, e.g., in dwelling- 

 rooms. In the latter case it is very difficult to keep up 

 the necessary concentration, and to have the vapour 

 equally divided through the whole^room. 



In disinfection with chlorine it is best to employ for 

 every cubic metre of space '25 kilo of chloride of lime 

 -f "35 kilo of crude hydrochloric acid. The material is 



