MICROSCOPICAL AND PHYSIOLOGICAL EXAMINATION. 17 



even when strongly diluted (25 per cent, of chlorine), is a 

 very efficient disinfectant, owing to its deadly action on fungi. 

 This substance being very cheap is therefore specially suited 

 for cleaning walls, pavements, gutters, etc. Bisulphite of lime 

 is also very efficient ; that of commerce usually contains 7 per 

 cent, of sulphurous acid, and is, when put into use, diluted 

 with a two- or threefold volume of water. This substance 

 is specially commendable for cleaning tuns and casks. 

 The filter-bags which, according to the investigations of 

 WILL, often contain very considerable accumulations of wild 

 yeasts and bacteria in the very texture of the material, and 

 which in many breweries are never sufficiently cleansed 

 should be disinfected by treatment with a solution of chloride 

 of lime. ( WILL, who experimented with material obtained 

 from a brewery, recommends a solution containing 1 per 

 cent, of active chlorine (corresponding to about 3-3 J kg. 

 of good commercial chloride of lime to 100 litres of water). 

 The aqueous mixture is stirred several times, and after deposi- 

 tion, the clear liquor containing chlorine is drawn off and put 

 into use. The filter-bags must be washed with pure water 

 after this treatment. In physiological laboratories, where it is 

 of especial importance to guard against any invasion of foreign 

 germs, an alcoholic solution of salicylic acid will prove of service 

 (it is often used by HANSEN in the Carlsberg laboratory for 

 cleaning tables). The action of this substance, in checking fer- 

 mentation even in a diluted state, is generally known. In the case 

 of very dirty tuns it is advisable to apply a very dilute alcoholic 

 solution of salicylic acid, and, after some time, to rinse thoroughly, 

 first with soda solution, and then with pure water. Eecently, 

 hydrofluoric acid has also been employed as a disinfectant. 



Among substances which have recently come into use for 

 this purpose, formaldehyde occupies a prominent place. This 

 gas is prepared commercially as a 40 per cent, solution called 

 formaline. Its power of killing bacteria is not inferior to that 

 of sublimate, while at the same time it is less dangerous to the 

 human system and that of the higher animals. The disinfec- 

 tion is effected in one of two ways : Cotton- wool or pieces 

 of cloth are moistened with the solution and hung up 

 in the infected locality ; or specially constructed lamps are 



