LABORATORY STERILIZATION 279 
ing soda (commercial sodium carlwnate) is even more efficient if 
applied hot, but there are limitations to its use. Fine furnishings 
and hangings, wall paper and similar o})jects cannot ordinarily be 
treated with liquid disinfectants. 
Testing and Standardizing Liquid Disinfectants.'— The first satis- 
factory method of comparing the disinfectant \alue of chemical dis- 
infectants was that of llideal and Walker,- widely known as the 
"Carbolic Coefficient" method. A modification of this method, pro- 
posed by Anderson and IVIcClintic,^ is widely used in the United 
States. Briefly, the method as modified by Anderson and McClintic 
consists in comparing the activity of the unknown disinfectant solu- 
tion in various dilutions with a standard solution of carbolic acid; 
B. typhosus is the organism selected for the purpose, and the strength 
of solution of both the unknown and known solutions is carefully 
measured. The time and temperature of exposure of the organism to 
the disinfectant solutions and the nature of the medium in which the 
exposure is made are carefully controlled. Even with the most 
rigorous attention to details, the carbolic coefficient of the same 
disinfectant determined by this method varies nearly 50 per cent in 
the hands of dift'erent observers.^ For the present, the standards of 
the Public Health and Marine-Hospital Service* are regarded as 
oflRcial for the United States. Kendall and Edwards'^ have described 
a method for the study of the penetrating power of disinfectants. 
Gaseous Disinfectants.— Pathogenic bacteria which are known or 
suspected to })e present upon fabrics or furnishings injured by chemical 
disinfectant solutions, as well as bacteria promiscuously distributed 
in rooms through droplet infection and by dust, may be killed by 
gaseous disinfectants, of which several are available. 
1. Formaldehyde.— Formaldehyde is the most efficient of the gaseous 
disinfectants for superficial disinfection, but its limited power of 
penetration must be borne in mind. Formaldehyde is dispensed 
commercially under the name "formalin," which signifies theoretically 
a 40 per cent volume solution of the gas (formaldehyde) in water. Com- 
mercial formalin rarely contains more than 36 per cent of formaldehyde 
by volume, however, and in practice it is well to estimate 35 per 
cent as a working basis. Commercial solutions, it must be remem- 
bered, are always acid, and the gas itself in small amounts is irritating 
to mucous membranes. Prolonged exposure to concentrations of the 
gas sufficient to kill bacteria may be fatal to animals. The gas has 
practically no insect icidal value. In sufficient concentration the gas 
is inflammable and may be ignited by any free flame. 
1 Chick: An Investigation of the Laws of Disinfection, Jour. Hyg., 1908, 8, 92. 
2 Jour. Sanitary Institute, London, 1903, 24, 424. 
' Bull. Hyg. Lab., Washington, D. C, April, 1912, No. 82. Full details of method 
and the disinfectant value of a large number of substances are given. 
* Hamilton and Ohno: Am. Jour. Pub. Health, 1913, 3, 582; ibid., 1914, 4, 163. 
5 Bull. Hyg. Lab., Washington, D. C, April, 1912, No. 82. 
6 Jour. Infec. Dis., 1911, 8, 250. 
