88 BIOLOGY AND TECHNIQUE 



ganate of potash in which they are rubbed with a sponge or sterile 

 cotton. They are then transferred to a saturated solution of oxalic acid, 

 until the red color has entirely disappeared. Following this, they are 

 rinsed in sterile water and then immersed in a 1 : 500 bichloride of 

 mercury solution for one to two minutes. 



According to Ftirbringer's method, the finger nails are carefully 

 cleaned with an orange-wood stick or nail file; the hands are then thor- 

 oughly brushed with a nail brush in green soap and hot water for five 

 minutes. Following this they are immersed in 60 per cent alcohol for 

 one minute, then in 3 per cent carbolic acid solution for one minute; 

 after which they are rinsed in sterile water and dried. 



Rooms, closets, and other closed spaces which are contaminated, must 

 be disinfected largely by gaseous disinfectants. After such disinfection 

 in the case of cellars, privies, and other places where feasible, walls and 

 ceihngs should be whitewashed. 



Gaseous Disinfectants for Purposes of Fumigation. — There are a 

 large number of gaseous agents which are harmful to bacteria. Only a 

 few, however, are of sufficient bactericidal strength to be of practical 

 importance. 



Oxygen, especially in the nascent state, may exert distinct bacteri- 

 cidal action upon some bacteria. That strictly anaerobic strains are 

 inhibited by its presence has already been mentioned. 



Ozone was shown by Ransome and Fullerton ' to exert considerable 

 germicidal power when passed through a liquid medium in which bac- 

 teria were suspended, but was absolutely without activity when em- 

 ployed in the dry state. 



Chlorine because of its powerful germicidal action was once looked 

 upon with favor, but has been found quite inadequate from a practical 

 point of view because of its injurious action upon materials, and its 

 irregularity of action. Chlorine, too, is but weakly efficient unless in 

 the presence of moisture.^ 



Sulphur dioxide or sulphurous anhydrid (SO2), which was formerly 

 much used for room disinfection, is no longer regarded as uniformly ef- 

 ficient for general use. The gas is produced by burning ordinary roll 

 sulphur. In order that it shall be at all effective, water should be 

 vaporized at the same time, since the disinfectant action is dependent 

 upon the formation of sulphurous acid. The concentration of the gas 

 should be at least 8 per cent of the volume of air in the room. For this 



' Ransome and Fullerton, Rep. Public Health, July, 1901. 



^ Fischer und Proskauer, Mitt. a. d. kais. Gesundheitsamt, x, 11, 1882. 



