DISINFECTANTS AND DISINFECTION 327 



dissociated by electrolysis the stronger is its disinfecting power. It 

 follows that anything which interferes with the electrolytical dissociation 

 of germicides weakens the germicidal power. For example, the addition of 

 sodium chloride lowers the germ destroying powers of corrosive sublimate 

 through such interference. This is a matter of great importance in 

 determining the efficiency value of antiseptics. 



7. The chemical composition of the material associated with the germs 

 to be destroyed, has a marked influence upon the action of the germicides. 

 Thus germicides give different results when acting upon the same organism 

 in water, in beef broth, in salt solutions, in and upon tissues, etc. For 

 this reason the value of germicides in actual practice cannot be based 

 exactly upon uniform laboratory results. 



8. Not only do different species of disease germs differ in resistance to 

 germicides, but the different strains of the same species react differently 

 with the same germicide. Certain substances appear to have an elective 

 affinity for certain organisms, as for example, quinine for the malaria germ, 

 and mercury salts for the syphilis germ. 



Disinfectants destroy or kill germs in different ways. In some cases 

 the death of the organism is due to oxidation as when ozone, hydrogen 

 peroxide and sulphites are used, or death may be due to interference with 

 nutrition, but more generally it is due to the coagulation of albumen and 

 abstraction of water from the cell-plasm, as in the use of dry heat, phenol, 

 alcohol, tannic acid and metallic salts. As already explained in another 

 chapter, lysins act by actually disintegrating the bacterial cells. 



As a rule germicides are most active when dissolved in water, though 

 some authorities declare that bichoride of mercury, phenol, thymol and 

 lysol are more active when dissolved in 50 per cent, alcohol. The activity 

 of phenol as a germicide is greatly increased by the addition of hydrochloric 

 acid, whereas lime reduces its potency. Solutions of germicides in oils 

 are inert because oil does not penetrate the bacterial cell; however, the oil 

 itself may be fatal to bacterial life, in which case the added germicide is 

 unnecessary. Chemical germicides do, however, increase the potency of 

 the volatile coal-tar products as gasoline, benzine and xylol, provided the 

 germicides are soluble in or readily miscible with these substances. 



The following are the more important disinfectants given approxi- 

 mately in the order of their usefulness and potency. 



a. Carbolic Acid (Phenol). Very widely used, in strengths of from 

 i to 5 per cent. As a disinfecting wash for all manner of septic things, a 

 5 per cent, solution is commonly employed. A 2.5 per cent, (also the 5 

 per cent.) solution is much used as a disinfectant for hands and the skin 

 generally and for septic wound irrigation. A 0.5 to i per cent, solution is 

 used as a mouth wash and gargle. Phenol does not kill spores hence 



