HO PRINCIPLES OF BACTERIOLOGY 



The Disinfecting Properties of the More Commonly Used 



Disinfectants. 



Bichloride of Mercury. This substance, when present in 1 part in 

 1,000,000 nutrient gelatin or bouillon, prevents the development of 

 parasitic bacteria. In water 1 part in 500,000 will kill many varieties 

 in a few minutes, but in bouillon twenty-four hours may be needed. 

 With organic substances its power is lessened, so that 1 part to 1000 

 may be required. Most spores are killed in 1 : 1000 watery solution 

 within one hour. Corrosive sublimate, as already noted, is less effective 

 as a germicide in alkaline fluids containing much albuminous substance 

 than in watery solution. In such fluids, besides loss in other ways, 

 precipitates of albuminate of mercury are formed which are at first 

 insoluble, so that a part of the mercuric salt does not really exert any 

 action. In alkaline solutions, such as blood, blood serum, pus, tissue 

 fluids, etc., the soluble compounds of mercury are converted into oxides 

 or hydroxides. The soluble compounds can, of course, remain in solu- 

 tion only when there are present sufficient quantities of certain bodies 

 which render solution possible. Bodies of this sort are especially 

 the alkaline chlorides and iodides, and, above all, sodium chloride and 

 ammonium chloride. A very simple way of preventing precipitation 

 of the mercury, then, is to add a suitable quantity of common salt to 

 the corrosive sublimate. Those compounds of mercury which, like 

 the cyanides, are not precipitated with alkalies, because they at once 

 form double salts, require no addition of salt. 



For ordinary use, where corrosive sublimate is employed, solutions 

 of 1 : 500 and 1 : 1000 will suffice, when brought in contact with 

 bacteria in that strength, to kill the vegetative forms within fifteen 

 minutes, the stronger solution to be used when much organic matter 

 is present. 



Biniodide of Mercury. This salt is very similar in its effects to the 

 bichloride. It is somewhat more powerful. 



Nitrate of Silver. Nitrate of silver in solution has about one-fourth 

 the value of the bichloride of mercury as a disinfectant, but nearly the 

 same value in inhibiting growth. 



Sulphate of Copper. This salt has about 50 per cent, of the value of j 

 mercuric chloride. It has a quite remarkable affinity for many forms of 

 algae, so that when in water 1 : 1,000,000 it destroys many forms; 1 : 400,000 

 destroys typhoid bacilli in twenty-four hours when the water has no 

 excessive amount of organic material. It is not known to be poisonous 

 in this strength, so that it can be temporarily added to water supplies. 



Sulphate of Iron. This is a much less powerful disinfectant than 

 sulphate of copper. 



Sodium Compounds. A 30 per cent, solution of NaOH kills anthrax 

 spores in about ten minutes, and in 4 per cent, in about forty-five minutes. 

 Sodium carbonate kills spores with difficulty even in concentrated solu- 

 tion, but at 85 C. it kills spores in from eight to ten minutes. A 5 per 

 cent, solution kills in a short time the vegetative forms of bacteria. 



