256 AIDS TO BACTERIOLOGY 



(2) the temperature of the room should not fall below 

 50 F., the best temperature being from 68 to 77 F.; 

 and (3) the strength of the formalin should be ascertained. 



Ethyl alcohol in from 20 to 50 per cent, solution is 

 germicidal for many vegetative forms of bacteria. - Stronger 

 mixtures generally have less effect in vitro, but, all the 

 same, rectified spirit is said to be admirable for the dis- 

 infection of the surgeon's hands. If bacteria thereon 

 are not quickly killed, it is argued that the alcohol fixes 

 them on the skin so effectively that they can only be 

 removed with difficulty (see also p/ 248). 



Picric acid is used for external disinfection in 0*5 per 

 cent, aqueous solution, especially after burns or scalds. 

 For wounds, Philip Turner recommends a 1 per cent, 

 solution in methylated spirit. Chloroform is used for 

 media (p. 39). Quite recently urea in strong solutions 

 has been recommended for antisepsis of wounds. 



Disinfectants of the Aromatic Series. Phenol (carbolic 

 acid) in saturated solution contains 6 to 7 per cent. 

 Proteins and organic matter generally only slightly 

 lessen its value. It is very poisonous and caustic, pro- 

 longed application to a surface producing ' carbolic acid 

 gangrene.' It is useless for sporing organisms, and is a 

 comparatively weak disinfectant. Its value in the arts is 

 such that very little of it is left in commercial carbolic 

 acid, which consists mainly of the cresols and higher 

 phenols. Cresols are only slightly soluble in water. A 

 mixture of ortho-, para-, and meta-cresols (tricresol) is 

 stronger and more soluble than individual cresols. 

 Cresols may also be dissolved in alkaline solution. 



Cresols are much reduced in efficiency by proteins. 

 In saturated salt solution the disinfectant value of crude 

 carbolic acid is greatly increased. With crude sulphuric 

 acid it forms, if the mixture is conducted under conditions 

 preventing any great rise of temperature, a substance 

 niiscible with water, and possessing strong disinfectant 

 activity. For disinfection and destruction of faeces this 

 sulphonated cresol may be used in 5 per cent, solution, 

 not, of course, in metal utensils. 



: Ordinarily neutral tar- oils with no appreciable dis- 

 infectant value are left in or mixed with tar distillate, and 

 the saponified product produces an emulsion with water. 

 Innumerable products of this type are made. Their 



