DISINFECTION BY HEAT 365 



of the use of superheated steam for disinfection was made 

 by Koch, who, in 1881, suggested raising steam from saline 

 solutions of boiling-points above 100° C. Disinfectors were 

 made on the Continent, working respectively with solutions 

 of salt and of calcium chloride, but were found unsatis- 

 factory. 



Steam is used either confined under pressure or as a 

 current with or without pressure. It is quite inaccurate to 

 speak of ' current steam ' as contrasted with steam under 

 pressure, as steam can be used as a current in either, with 

 or without a pressure exceeding that of the atmosphere. 

 The advantage of some amount of pressure of saturated 

 steam, however small, is that it gives a real control over 

 the temperature of steam, which in a well-designed disin- 

 fector is practically uniform throughout. It has also been 

 repeatedly shown that in the iabsence of pressure the tem- 

 perature and disinfectant value of the steam depends largely 

 on its velocity, and the rate of stoking will largely affect it 

 — an objection which is serious because there is no con- 

 venient or trustworthy means of controlling either the 

 velocity of the steam or the rate of stoking. What the 

 temperature should be is still a matter of discussion. 

 Many common bacteria, such as those of typhoid, diph- 

 theria, and cholera, are with certainty destroyed by almost 

 momentary exposure to temperatures below 100° C. This 

 is not the case with aU, dried tuberculous matter, for 

 instance, having been known to resist over three hours' 

 boiling; and our knowledge of the organisms producing 

 many diseases, for example small-pox and scarlet fever, is at 

 present insufficient to justify a definite statement of the 

 temperatures necessary for their disinfection. The latest 

 researches (Miquel and Lattraye) conclude that twenty 

 minutes' exposure to a temperature of 110° C. should be 

 allowed in all cases. It must be remembered, also, that in 



