THE DESTRUCTION OF BACTERIA 95 



readily in boiling dilute alcohol, the most effectual being propyl 

 alcohol of a concentration of from 10-40 per cent. 



CARBOLIC ACID (C 6 H 5 OH), at room temperature, consists of color- 

 less crystals which become completely liquefied by the addition of 

 10 per cent of water. In contradistinction to most inorganic dis- 

 infectants, the action of carbolic acid and other members of the 

 phenol group is not in any way dependent upon dissociation. 44 

 According to Beckmann 45 and others, carbolic acid acts as a mole- 

 cule and not by individual ions. The proof of this is brought out 

 by the fact that the addition of NaCl to carbolic acid solutions, 

 an addition which would tend to decrease the concentration of free 

 ions, markedly increases the bactericidal powers of such solutions. 

 On the other hand, as stated above, additions of alcohol progres- 

 sively diminish the efficiency of the phenols. 



Other members of this group of disinfectants are ORTHO-, META-, 

 and PARACRESOL (C 6 H 4 CH 3 OH), isomeric compounds differing only 

 in the position of the OH radicle. Tricresol is a mixture of these 

 three. The cresols are relatively more powerfully germicidal than 

 carbolic acid, but are less soluble in water. LYSOL is a substance 

 obtained by the solution of coal-tar cresol in neutral potassium-soap. 

 Dissolved in water it forms an opalescent easily flowing liquid. 

 According to Gruber, 46 its germicidal action is slightly greater than 

 that of carbolic acid. CREOLIN, another combination of the cresols 

 with potassic soap, forms with water a turbid emulsion, v. Behring 47 

 expressed the relative germicidal powers of carbolic acid, cresol, 

 and creolin for vegetative forms by the numbers 1 : 4 : 10, in the 

 order named. 



FORMALDEHYD (H-COH), or methyl aldehyde, is a gas which is 

 easily produced by the incomplete combustion of methyl alcohol. 

 The methods of actually generating it for purposes of fumigation 

 will be discussed in a subsequent paragraph. In aqueous solution 

 this substance forms a colorless liquid with a characteristic acrid 

 odor, and in this form is Jargely used as a preservative for animal 

 tissues and as a germicide. It is marketed as "formalin," which 

 is an aqueous solution containing from 35 to 40 per cent of the 



44 Scheuerlen und Spiro, Munch, med. Woch., 44, 1897. 



45 BecTcmann, Cent, f . Bakt., I, xx, 1896. 

 48 Gruber, Cent. f. Bakt, I., xi, 1892. 

 "v. Behring, loc. cit., p. 111. 



