72 MICROBIOLOGY 



cidal with young cultures. The disinfectants may be grouped 

 according to the condition in which they are applied as (1) 

 natural agents, (2) chemical solutions and (3) gases. 



The natural germicidal agents are sunlight and drying. 



The more commonly used disinfectants are bichloride of 

 mercury, carbolic acid (phenol), sulphur, calcium compounds, 

 formalin and the cresols. Formaldehyde and sulphur are used 

 in the form of gases. There are, however, many other prepa- 

 rations that are used, among which are equal parts of sul- 

 phuric and crude carbolic acid. 



Bichloride of mercury (HgCl 2 ) (Corrosive sublimate). 

 This is a white crystalline mass. It will dissolve in 16 parts 

 of cold water and 3 parts of hot water. As a germicide, bi- 

 chloride of mercury acts in solution by combining chemically 

 with the microprotein of the organisms. This requires direct 

 contact between the microorganisms and the solution in which 

 a, certain length of time and concentration of the solution are 

 necessary. Koch, 1 Sternberg 2 and many others have found 

 this to be a very powerful germicide. Its efficiency depends, 

 however, upon the nature of the medium in which the bacteria 

 .are when subjected to its influence. For ordinary disinfection 

 an aqueous solution of 1 to 1000 is used. The addition of a 

 small quantity of common salt is desirable to avoid crystal- 

 lization. Sixty grains of corrosive sublimate and two table- 

 spoonfuls of common salt to one gallon of hot water make a 

 solution of 1 to 1000. When it is employed to disinfect sub- 

 stances containing albuminous matter such as sputum or feces 

 it must be used in excess as a chemical combination takes place 

 between the mercuric chloride and the albuminous matter 

 present. Behring :! found that this solution would kill vege- 

 tating anthrax bacteria in a- dilution cf 1 to 500,000. It must 

 not be kept in metal retairers but in those of glass or wood. 



1 Koch. Mitt. a. d. K^is. Cerurdheit, Bd. I (1881) p. 269. Trans- 

 lated in Recent essays New Sydenham Society 1886. 



2 Sternberg. Disinfection and Disinfectants, 1888, p. 41. 



3 Behring. Bekampfimg der Infectionskrankheiten. Bd. II 

 <1894) p. 43. 



