i8o Sterilization and Disinfection 



germicidal action of the' mercuric salt about one-half. Notwithstanding this, 

 however, the "antiseptic tablets" in common use for surgical and household 

 purposes contain one or both of these salts, added for the purpose of preventing 

 the precipitation of the mercuric compounds formed in the presence of alkaline 

 albuminous materials, such as blood, pus, sputum, feces, etc. 



The addition of about 25 per cent, of alcohol to the solution of the mercuric 

 salt greatly enhances its value. Strong alcoholic solutions are, however, less 

 useful than aqueous solutions, for the 95 or 100 per cent, alcohol dehydrates the 

 micro-organisms and prevents the diffusion currents by which the mercury is 

 carried into their substance. 



For most purposes a i : 2000 solution of the mercuric chlorid is to be recom- 

 mended. 



Silver Nitrate (AgNOa). — The solutions of this salt are probably more 

 useful than the frequency of their employment might suggest. They 

 have, however, the disadvantages of decomposing when kept in the 

 light and of making black stains when applied in concentrated form 

 to the skin or dressings. 



The germicidal power of the salt in aqueous solution is less than that 

 of the mercuric chlorid, but the power in albuminous fluids in greater. 

 Anthrax spores in blood-serum are killed in seventy hours in a i : 12,000 

 solution. The addition of other salts, as ammonium salts, interfere 

 with the germicidal activity by inhibiting ionization. 



Combinations of the silver nitrate with albuminous compounds, and 

 variously known as argonin, argentum casein, argyrol, protargol, etc., 

 have been used where the disinfecting power of the silver is sought for 

 with the least amount of irritation and the deepest 'degree of pene- 

 tration, as in the treatment of gonorrhea. 

 Potassium Permanganate (KMn04). — Solutions of this salt seem to act by 

 virtue of a strong oxidizing power. In 2 per cent, solutions anthrax 

 spores are killed in forty minutes; in 4 per cent, solutions, within 

 fifteen minutes. Koch's experiments showed less activity of the germi- 

 cidal power against anthrax spores. In his hands a s per cent, solution 

 seemed to require about a day to effect complete destruction. A i per 

 cent, solution kills the pus cocci in ten minutes; a i : 10,000 solution 

 kills plague bacilli in five minutes. 



The chief difficulty is that the salt is quickly reduced and its strength 

 destroyed by the organic substrata in which the bacteria are contained. 

 Halogens and Compounds. — Those with the lowest atomic weight have 

 the greatest disinfecting power. 

 Chlorin.—Thh is usually -employed in the form of chlorinated lime. It 

 seems to be a mixture of calcium hj^ochlorite, Ca(C102), and calcium 

 chlorid, CaOCl2. The addition of any acid, including the atmospheric 

 CO2, causes the evolution of CI. The powder is readily soluble and 

 solutions of I : 500 kill vegetative forms of most bacteria in a few 

 minutes (not, however, resisting spores). 



A proprietary compound known as "electrozone," made by electro- 

 lyzing sea-water in such a manner that magnesia and chlorin are liber- 

 ated and magnesium hypochlorite and magnesium chlorid formed, is a 

 cheap and useful chlorin disinfectant. Nissen found that 1.5 per cent, 

 of it killed typhoid bacilli in a few minutes; Rideal, that i 1400 to 500 

 dilutions of it disinfected sewage in fifteen minutes; and Del^pine, that 

 I : 50 (equal to 0.66 per cent, of chlorin) rapidly killed the tubercle 

 bacillus and i : 10 (equal to 3.3 per cent, chlorin) killed anthrax spores. 

 lodin Terchlorid (ICI3). — This compound, which is so unstable that it 

 only keeps in an atmosphere of Cl-gas, has great germicidal action, 

 that probably depends upon the readiness with which it decomposes. 

 In solutions of i : 1000 it kills vegetative bacteria in a few minutes, 

 and in i : 100 it kills anthrax spores with equal rapidity. The presence 

 of organic and albuminous materials does not interfere with the germi- 

 cidal action. 



Organic Disinfectants. 



Carbolic Acid (CeHsOH) is the most important and generally useful of 

 these. It has the advantage of being cheap and easily kept and 

 handled. In the pure state it consists of colorless acicular crystals. 



