148 PRACTICAL DAIRY BACTERIOLOGY 



The preservatives that have been most commonly used for the 

 purpose may, however, be briefly mentioned. The most com- 

 mon in use in this country is formalin. This is a clear liquid, 

 which is a very efficient germicide, and is the basis of most, if 

 not all, of the liquid preservatives on the market under different 

 names. It is very efficient as a preservative of milk, even as 

 small a quantity as one part in 40,000 (one teaspoonful to 15 

 gallons of milk) noticeably enhancing its keeping property. 1 

 Whether this small amount injures the digestibility of he milk 

 is not yet settled, 2 although in general formalin makes proteids 

 difficult to digest, even one part to 2,000 being said to do so. 

 But at all events formalin is an adulterant and, as such, for- 

 bidden by law in most places in the country. It is easily 

 detected in milk by chemical means. 3 Borax, boracic acid 

 and salycilic acid have also been used, but they are all even 

 more objectionable than formalin. Most of the preservatives of 

 the market put up in powdered form contain one or more of 

 these substances. 



The use of hydrogen peroxide (H 2 O 2 ) has been very strong- 

 ly urged in recent years as a preservative in milk. 4 This 

 material, when added in small quantity, about one gram per 

 liter (i oz. to 9 gals.) has the advantage of rapidly disappearing 

 from the milk, especially if subsequently heated. 5 After being 

 in the milk for a little, one atom of oxygen that it contains is 

 loosened and passes off, leaving the substance as plain water H 2 O. 

 Meantime it has destroyed most of the bacteria. It seems 

 to be an efficient and perfectly harmless preservative. It is, 



1 Lowenstein. Zeit. f. Hyg., xlviii., p. 239, 1904. 

 Schaps. Zeit. f. Hyg., 1., p. 247, 1905. 



2 Chester and Brown. Bui.. 71, Del. Exper. Sta., 1905. 

 Trillat. Rev. Gen. d'Lait, III., p. 380, 1904. 



3 Eury. Milchw. Zent., Hi., p. 173, 1907. 

 4 Budde. Nord. Mejeri. Tidn., 1903. 



Barthel. Nord. Mejeri. Tidn., 1893; also Rev. Gen. d'Lait, II., p. 289, 1903. 

 5 Rosam-Pilsen. Cent. f. Bact., II., viii., p. 769, 1902. 



Lukin. Cent. f. Bact., II., xv., p. 20, 1905. 



