98 MILK AND DAIRY PRODUCTS PART 



with freshly prepared ones, there are no peroxides, and, in 

 consequence, no blue coloration is given. This fault can of 

 course be remedied by adding a peroxide when making the 

 test, and the most suitable substance is a few drops of hydrogen 

 peroxide. 



Instead of tincture of guaiacum, Dupoy, 1 has proposed an 

 aqueous solution of guaiacol. If the milk has not been heated, 

 then a distinct orange coloration is given if 1 c.c. of aqueous 

 guaiacol solution (1 per cent.) and one drop of hydrogen 

 peroxide (3 per cent.) are added to 1 c.c. of the milk. When 

 the milk has been heated to at least 80 C. there is no 

 coloration. 



(b) Starch's Paraphenylene Diamine Test. 



V. Storch 2 makes use of the property which milk possesses 

 of decomposing hydrogen peroxide as was discovered by 

 Babcock 3 in 1889. The course of the decomposition is, 

 according to Babcock and Russell, a tryptic ferment which 

 they call Galactase (see p. 12). Latterly other enzymes have 

 been shown to exist in milk, namely Catalase and Peroxidase, 

 and to these has been ascribed the power of decomposing 

 hydrogen peroxide. The author 4 is of the opinion that it is 

 the innumerable white blood corpuscles, the so-called leuco- 

 cytes, in the milk which are the carriers of the enzymes that 

 decompose hydrogen peroxide, and give colour reactions with 

 guaiacum, paraphenylene diamine, &c. When milk is separated 

 some of the leucocytes pass into the cream, but the greater part 

 remain in the separator slime, of which they form an important 

 constituent 5 (see Fig. 48). Later investigations have proved 

 the truth of this view, although it must be allowed that the 

 micro-organisms in the milk greatly assist in producing 

 catalase. 



Storch found that of all the reagents which come into 

 question for proving if a milk has been heated to 80 C., the 

 best was paraphenylene diamine. This compound gives ordina- 

 rily a brown colour when acted upon by " active " oxygen, but 



1 Journal de pharmacie et de chimie, 1897, Vol. I, p. 397. 



2 40 Beretning fra den Kgl, Vet. oy Landbohojskoles Laboratorium for 

 landokonomiske, Forso'j, 1898. 



' Bulletin No. 18, Agile. Expt. Stat., Univ. of Wisconsin, 1889. 



4 Nord. Mej.-Tidning, 1899, No. 16. Ref., MUch-Zeitnny, 1899, No. 31. 



5 Chr. Barthel. " Sur la composition de la boue de centrifuge," JRevue G6n. 

 du Lait, Vol. I, p. 193. 



