180 BACTERIOLOGY. 



A fairly high /temperature but one still below that 

 which would injure delicate fabrics increases not only 

 the activity of formaldehyde gas but also its penetra- 

 tive power, and for heavy goods it is essential. The 

 production of a partial vacuum in the chambers be- 

 fore the introduction of the formaldehyde gas still 

 further assists its penetration. 



The length of exposure necessary for complete dis- 

 infection depends upon the nature of the disease for 

 which it is carried out the penetration required, the 

 concentration of the gas used, the amount of moisture 

 in the air, the temperature of the air, and the size and 

 shape of the room. For surface disinfection in rooms, 

 when as much as 12 ounces of formalin are used for 

 each 1000 cubic feet, five hours' exposure is amply 

 sufficient, most bacteria being killed within the first 

 few minutes. For the destruction of micro-organisms 

 protected by even a layer of thin covering, double the 

 formalin and double the time of exposure should be 

 allowed, and even then the killing of many species of 

 non-spore bearing bacteria cannot be counted upon 

 in ordinary rooms. When absolutely complete disinfec- 

 tion is demanded, where penetration of gas is required, 

 the goods must be placed in chambers where moderate 

 heat can be added and all leakage of gas prevented. 



Various forms of apparatus can be properly employed 

 to liberate formaldehyde gas for purposes of disinfec- 

 tion, as each of these is lauded by its maker as the 

 best; it may be of interest to give the results obtained 

 by us from those in most common use. There are two 

 essentials to any good method namely, that the for- 

 maldehyde gas is given off quickly; and that there is 

 no great loss by deterioration of the formalin. 



