334 BACTERIA 



spirit to produce the gas. Hence we have three common 

 forms of the same thing — formalin, formic aldehyde, para- 

 form — each of which y\^^'=> formic acid, and thus disinfects. 

 The vapour cannot in practice be generated from the forma- 

 lin as readily as from the paraform. 



By a variety of ingenious arrangements formic aldehyde 

 has been tested by a large number of observers during the 

 last two or three years. We may refer to three modes of 

 application, i. The sprayer (Equifex apparatus) produces 

 a mixture of air and solution for spraying walls, ceilings, 

 floors, and sometimes garments. 2. The autoclave (Trillat's 

 apparatus). In this a mixture of a 30-40 per cent, watery 

 solution of formaldehyde and calcium chloride (4-5 per 

 cent.) is heated under a pressure of three or four atmos- 

 pheres, and the almost pure, dry gas is conducted through 

 a tube passing through the keyhole of the door into the 

 sealed-up room. 3. The paraform lamp (the Alformant). 

 The principle of this lamp is that the hot, moist products 

 from the combustion of methylated spirit act upon the para- 

 form tablets, converting them into gas. Most of the con- 

 clusions derived from experiments with these three different 

 forms of apparatus are the same. It is agreed that the gas 

 is harmless to colours and metal and polished wood. The 

 vapour acts best in a warm atmosphere. As for its action 

 on bacteria, it compares favourably with any other disinfect- 

 ant. In I per cent, solution formalin destroys non-spore- 

 bearing bacteria in thirty to sixty minutes. 



Many observers have decried formaldehyde on account of 

 its professed lack of penetrating power. Professor Del^pine, 

 however, states ^ that it possesses '' penetration powers prob- 

 ably greater than those of most other active gaseous disin- 

 fectants. Bacillus coli, B, tuberculosis, B. pyocyaneus, and 

 Staph, pyogenes aureus were killed in dry or moist state, 

 even when protected by three layers of filter paper. *' In 



^ Journal of State Medicine^ 1898 (November), p. 541. 



