92 OUTLINES OF BACTERIOLOGY 



after one minute. As a wash for the hands it is sufficient to use a 

 3 per cent, solution, and a 5 per cent, solution will effectively sterilise 

 objects immersed in it. 



Formalin. This substance is a 40 per cent, solution of formal- 

 dehyde. It can destroy the non-sporogenous cells of typhosus, anthrax, 

 and cholera in a very weak solution. It is claimed that a teaspoonful 

 of it is sufficient to prevent the souring of 10 gallons of milk. The 

 substance called paraform is the white residue obtained by the evapo- 

 ration of formalin. This powder is made up into lozenges, which are 

 used in the preparation of formalin fumes by being burnt in methy- 

 lated spirits : the fumes are easier to obtain from paraform than from 

 formalin itself. Of late years several contrivances have appeared on 

 the market to facilitate the production of this vapour. 



1. Sprayer. This produces a mixture of air and fine particles of the 



solution, and is useful for spraying walls, floors, and sometimes 

 garments. There are several forms on the market. 



2. The Autoclave (Trillat's apparatus). In this apparatus a mixture 



of 30-40 per cent, aqueous solution of formalin and 4-5 per cent, 

 calcium chloride is heated under pressure of 3-4 atmospheres. 

 The vapour is usually passed through the keyhole of a sealed-up 

 room, which is thus subjected to a vapour in all its parts. 



3. The Para/win Lamp (the Alformant). Paraform in the form of 



tablets is subjected to the action of the vapour produced by the 

 combustion of methylated spirit. When saturated with para- 

 form, this vapour is a very effective disinfectant. 



4. Lingner's Apparatus. Steam is generated in a ring boiler and 



then driven into a reservoir containing formalin or glycoformal 

 (30 per cent, formalin and 10 per cent, glycerine). The 

 resulting vapour is ejected in the form of a fine spray through 

 four nozzles, and fills the room with a thick vapour. Houston 

 and Newman found that after 4 hours' exposure Bac. pyocyaneus, 

 Staphylococcus pyogenes aureus, and other organisms were 

 destroyed. Klein and Newman also found that Bac. anthracis 

 and the bacillus of consumption were killed by the same means. 

 It has also been claimed that anthrax spores can be killed by 

 vapourising per cubic metre 7*5 c.c. of formalin with four times 

 its volume of water, the exposure which is necessary being not 

 more than 6 hours. 



It is obvious, then, that we have in formalin an extremely useful 

 disinfectant. The objection to it in the vapour condition is that it 

 has an irritating effect on the mucous membrane of the nose and 



