78 BIOLOGY AND TECHNIQUE 



not in any way dependent upon dissociation/ According to Beckmann ^ 

 and others, carbolic acid acts as a molecule 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, addi- 

 tions of alcohol progressively diminish the efficiency of the phenols. 



Other members of this group of disinfectants are ortho-, meta-, and 

 PARACRESOL (C„H4CH30H) , 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 is 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 Gru- 

 ber,' 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 * expressed the relative 

 germicidal powers of carbolic acid, cresol, and creolin for vegetative 

 forms by the numbers 1:4 : 10, in the order named. 



Formaldehyde (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 largely 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 gas and which exerts distinctly bactericidal 

 action on vegetative forms in further dilutions of from 1 to 10 to 1 to 

 20 (formaldehyde gas 1 : 400 to 1 : 800) . Anthrax spores are killed 

 in 35 per cent formaldehyde in ten to thirty minutes.^ Unlike the 

 phenols, the addition of salt to formaldehyde solutions does not increase 

 its efficiency, but similar to them, additions of ethyl and methyl alcohol 

 markedly reduce its germicidal powers. 



The essential oils which are most commonly used in practice — 

 largely as intestinal antiseptics — are those of cinnamon, thyme, eucalyp- 



' Scheuerhn und Spiro, Munch, med. Woch., 44, 1897. 



2 Beckmann, Cent. f. Bakt., I, xx, 1896. 



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

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



' KrSnig und Paid, loc, cit. 



