DISINFECTION BY CHLORINE 361 



numberless small organised vegetable structures, the death 

 of all of which can be assured if they are brought into 

 contact with the proper reagents. 



Apart from the low specific disinfectant value of such 

 gases, they must in practice become diluted to an uncertain 

 extent, which increases continually during the operation ; 

 the process of diffusion by which they penetrate to various 

 parts of the room under treatment gives a disinfectant 

 atmosphere of varying and uncertain composition ; and the 

 presence of any slight mechanical obstacle, such as a little 

 dust or flue, may be sufficient to protect organisms from 

 being disinfected. A disinfectant spray, on the other hand, 

 has a known initial strength, which continually increases 

 during drying ; it is brought directly in contact with the 

 organisms on the surface to be disinfected ; and when 

 applied by a suitable apparatus, such, for instance as the 

 Equifex sprayer, it is projected on to the surface with a 

 sufficient velocity to penetrate obstacles which would 

 protect against the action of a gas or vapour. 



Disinfection by Formic Aldehyde (Formalin) Vapour. — 

 Formic aldehyde is a gas possessing a high disinfectant 

 power but practically no capacity for penetration. It is 

 liable to change into a polymeric form possessing relatively 

 little disinfectant power. It has been proposed to use it 

 for disinfectant purposes in three principal ways ; in the 

 one by the generating it by the combustion of methylated 

 spirit in a special lamp admitting a regulated quantity of 

 air; in the second by the heating under a pressure of 

 3 to 4 atmospheres of a mixture of formaldehyde solution 

 and calcium chloride (Trillat's autoclave) ; and by the 

 volatilisation of paraform tablets. The best results have 

 been obtained from the Trillat autoclave, the gas being 

 conducted from it by a tube passing through the keyhole 

 of the door into the room, which has to be carefully sealed, 



