108 REPORTS ON THE STATE OF SCIENCE.—1918. 
Cf. Ber. des. Versuchst. d. K. Vet. u. Landb. Hochs., Kopenhagen ; 
Milchztg., 27, 374 (1898). 
A grey-blue coloration is given. It is necessary for this test, how- 
ever, to use only 1 drop of H2O2 inasmuch as boiled cows’ milk gives 
a blue coloration with p-phenylene-diamine and H,Ok,, if the latter 
is present in sufficient quantity. This is owing to the fact that the 
casein interacts with an oxidation product of the amine giving a blue 
compound. Such a milk would not respond to the guaiacol test, 
unless a peroxidase were added. Cf. Nicolas, Bull. Soc. Chim. 9, 
266-269 (1911-14). ; 
The importance of the “peroxidase reaction” in the colloid 
chemistry of milk lies in the fact that most investigators now believe 
peroxidase to be a peculiarly active form of ‘colloidal iron or 
manganese hydroxide, held in solution by a protective (hydrophile) 
colloid. 
This protective colloid or emulsoid stabilises the system, and very 
likely confers specific properties such as coagulation by heat, acids, 
alcohol, ete. See Perrin, J. de Chim. phys., 3, 103 (1905); also, 
Réhmann and Shnamine, Biochem. Zeits., 42, 235-249 (1912). 
Wolff, in his “ Contributions a la connaissance de divers phéno- 
menes ozydasiques naturels et artificiels” (1910), describes the full 
reproduction of all the actions of peroxidase with colloidal ferro- 
cyanide ofiron, Similarly, Sjolleman made an artificial oxidase with 
a colloidal solution of manganese hydroxide. 
Lactic acid and hydrogen peroxide only interact very slowly ; if 
now, a trace of ferrous sulphate be added, oxidation proceeds very 
rapidly indeed. A similar acceleration of oxidation can be brought 
about by addition of peroxidase. Thus the close similarity between 
the true inorganic colloid and the enzyme is shown clearly. In fact 
an artificial peroxidase of marked activity was described by Dony- 
Henault, Bull. de la classe d. Sciences, Acad. roy. de Belgique, 
pp. 105-163 (1908), viz., A solution of 10 yrs. gum-arabic, 1 gr. 
manganese formate and 0°4 gram. sodium bicarbonate in 50 ce. 
water, is treated with alcohol. The ppt. is redissolved and repre- 
cipitated by alcohol. The precipitate contains colloidal manganese 
hydroxide kept in stable solution by the “ protecting’? gum-arabic. 
The “ peroxidase reaction” is, no doubt, very closely connected 
with the iron content of milk, and it has been shown that there is 
quite sufficient iron in cows’ milk to produce the reaction. The 
amount of iron in milk varies from 0°4 to 0:7 mg. per litre. Cf. 
Edelstein and von Csonka, Biochem. Zt., 388, 14-22 (1912). 
Sarthou, Jour. de Pharm., 2, 583 (1910), and 8, 49 (1911), showed 
_ that the peroxidase reaction can result when as small a quantity as 
°0002% of iron is present. 
The reaction is used in dairy laboratories to detect between raw 
and pasteurised milk, and although great differences of opinion are 
held as to the temperature at which the reaction is no longer given, 
it is generally agreed that milk pasteurised by heating to at least 
70° ©. for about 15 minutes, renders the peroxidase inactive. Cf. 
van Keck, Zeit. f. Unters. Nahr. u. Genussm., 22, 393 (1911). 
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