250 AIDS TO BACTERIOLOGY 



when diluted many times is to be preferred, not only 

 because of the saving in storage and transit, but so that 

 in cases of necessity, as when sporing organisms require 

 disinfection, a stronger disinfectant dilution is permitted. 



2. Retention of efficiency in the presence of such 

 organic matter as is likely to be met with in practice. 

 Organisms are seldom offered for disinfection separate 

 from appreciable amounts of oxidisable organic matter, 

 and a disinfectant dependent for its efficiency on oxidation 

 properties wastes itself on dead matter more readily than 

 it attacks living protoplasm. 



3. Production of emulsion or solution in all proportions. 



4. Permanent homogeneity. Disinfectants of a certain 

 type separate out on standing or in cold weather into 

 layers very different in efficiency, and although a shilling 

 bottle may be rendered homogeneous by shaking, the 

 matter is less easy when a 40-gallon cask is concerned. 



5. Solvent power for grease. 



6. Stability at all reasonable temperatures, so as to 

 allow its use when heat is also available. 



7. Freedom from toxicity in all dilutions necessary for 

 complete disinfection. 



8. Non-caustic, non-corrosive, harmless to fabric, and 

 without action on dyes. 



Acids. All acids are disinfectants, the efficiency being 

 directly proportional to the degree of acidity. Sulphur 

 dioxide is obtained by burning sulphur ( ' Sulphur candles ' 

 are convenient), or from the liquefied gas. Plenty of 

 moisture is necessary in the atmosphere of the room or 

 ambulance to be disinfected, and a high temperature assists 

 the action. Its power of penetration can be taken as 

 practically nil, and its chief application at the present 

 time is the destruction of vermin, notably rats, which in 

 plague-infected ships and houses may often be desirable. 

 For this purpose the Clayton apparatus has been used, 

 but its high cost and somewhat complicated construction 

 have prevented it from obtaining an extended application. 

 Christian mentions that air containing 5 per cent, of 

 Clayton gas kills rats, fleas, and other vermin in a few 

 seconds, and when 1 per cent, only of the gas is present 

 the rats cannot reach their runs. (As an alternative, 

 Nocht and Giemsa proposed carbon monoxide for rat 

 destruction. This gas is not a disinfectant, though 



