MEANS FOR KILLING BACTERIA. 665 



of the whole mass of fluid to be disinfected to 100 C. ; 

 on the other hand it is easy, as Koch has shown, by 

 means of a current of steam to obtain the necessary 

 temperature of 100 C. in all sorts of materials. At the Action of a 

 bottom of the apparatus necessary for this purpose sto X1 m n 

 there is a large vessel, on the top of which a tube of 

 sheet zinc, 1 to 2 metres in height, is fixed ; this tube 

 is gradually narrowed at the top, and finally runs out 

 in the form of a short tube, only 1 cm. in diameter. 

 The zinc tube is fixed tightly on the top of the boiler, 

 and its outer surface is enveloped in some substance 

 which conducts heat badly. If the water in the boiler 

 is boiled, the steam passes out of the narrow upper 

 opening in a strong current, and from that opening 

 downwards the steam has a temperature of 100 C. If 

 now the objects to be disinfected are placed inside the 

 vertical tube they are rapidly penetrated by the steam 

 and raised to a temperature of 100, and even in a few 

 minutes the majority of the spores of bacilli are 

 destroyed. The duration of the heat must of course be 

 somewhat varied according to the nature of the materials. 

 Fresh tubercular sputum is disinfected with certainty in 

 about fifteen minutes, dried sputum in thirty to sixty 

 minutes. A duration of sixty minutes is sufficient to 

 kill the most resistant spores as yet known, even when 

 surrounded by a relatively dense mass of material. The 

 rapidity of the effect is increased by employing a salt 

 solution, and thus obtaining steam at a higher tempera- 

 ture than 100 C. 



A number of chemical poisons are also suitable for the Chemical 

 destruction of bacteria. With regard to these, we have p( 

 to note the concentration of the poison, the duration of 

 its action, the nature of the nutrient substrata and the 

 other conditions of life, and the specific resisting power of 

 the species, more especially the presence of resting forms. 

 Bacteria free from spores are on the whole destroyed 

 by very small proportions ; thus carbolic acid kills an- 

 thrax bacilli when in a concentration of '25 to '5 per 

 cent. ; 1 per cent, sulphurous acid kills them within five 

 to fifteen minutes. In the practical work of disinfection 



