638 A MANUAL OF BACTERIOLOGY 



or glycerine, by the depolymerisation by heat of the solid 

 polymer paraformaldehyde, or by mixing this substance 

 with potassium permanganate. Many forms of apparatus 

 have been designed for the production of formaldehyde gas 

 for disinfection. In any form the gas seems to give little 

 more than superficial disinfection, and to require precau- 

 tions to ensure diffusion throughout the atmosphere of a 

 room. The conditions desirable for disinfection by for- 

 maldehyde gas are saturation of the air with moisture, 

 maintenance of a good room temperature, sealing of the 

 room, the use of at least 60 grm. of formaldehyde per 

 1000 cubic feet (preferably more, up to 120 grm.), and in 

 the case of large rooms mixture of the gas with the air of 

 the room, either mechanically or by the provision of a 

 multiplicity of inlets for the gas into the atmosphere. By 

 the use of a vacuum formaldehyde can be evaporated in 

 a closed chamber at temperatures indifferent to many 

 substances which will not stand steam at 100, and con- 

 siderable penetration can be obtained (Defries process). 

 As a spray formalin can be used in any ordinary apparatus. 

 Formalin seems to have a very slow germicidal action, for 

 tested by the Rideal- Walker method, its carbolic co- 

 efficient is only about 0-7 for the B. typhosus. Yet 2 

 per cent, formalin kills anthrax spores in two or three 

 days and gaseous formaldehyde is similarly active. 



Of the aromatic series, the number of substances and 

 preparations is extraordinarily large. The standardisation 

 of methods of examination will, it is to be hoped, eliminate 

 the less efficient. 



The best known is phenol (carbolic acid). Its saturated 

 solution contains about 9 per cent. It is only slightly 

 affected by albuminoids, and generally is stable in the 

 presence of organic matter at ordinary temperatures. Its 

 compounds, when it forms any, have themselves some 

 disinfectant action. With acids this action is usually 



