SO-CALLED ' BIOLOGICAL PROPERTIES ' OF MILK 69 



to have been made in the year 1868 by Klebs, since when there 

 has been a continuous succession of papers dealing with one aspect 

 or another of its activity. For many years it was believed that 

 there were two ferments present in milk, both acting as oxidising 

 agents that is, they were both capable of increasing the amount 

 of oxygen in certain substances, but had slightly different actions. 

 This belief appears to have been due to the fact that different 

 reactions were obtained according as the test solution had been 

 allowed to stand for some time before using or not. 



The method of testing for this ferment which was first used, 

 was to add guaiacum tincture to milk. In certain cases the milk 

 at once turned blue. In others this blue reaction was only brought 

 about after hydrogen peroxide had also been added. It seems 

 clear as a result of later observations that the difference arose 

 from the fact that when guaiacum tincture is allowed to stand, 

 a substance develops in it which can take the part of hydrogen 

 peroxide and produce the blue colour at once without the addition 

 of this substance. Guaiacum tincture is not so much used at the 

 present time, since Storch, whose investigations have already 

 been alluded to, discovered that a more reliable reaction was 

 obtained when the substance known as para-phenylene-diamine 

 was used, instead of the guaiacum tincture. It has already been 

 mentioned that this reaction results in the formation of a grey-blue 

 coloration in the milk. A number of other substances are now 

 used to replace or act as supplementary tests to the para-phenylene- 

 diamine. Many of these substances strike extremely brilliant 

 colours in the milk, and are believed by many to be equally reliable. 

 In this country, however, the peroxidase test appears to be most 

 usually carried out with para-phenylene-diamine, and this method 

 will be regarded as the recognised one in the following remarks. 



On the Presence of Peroxidase in Cows* Milk. This ferment 

 appears to be universally present in cows' milk. It is also widely 

 distributed throughout the entire animal and vegetable kingdoms, 

 being found in a very great number of vegetable tissues as well 

 as in most animal tissues. It is present in blood in considerable 

 quantities ; in fact, a common test for the presence of blood is 

 the test above alluded to, with guaiacum tincture. The desirability 

 of possessing a reliable test for milk which has been heated is so 

 evident as to need no further consideration. It applies equally in 

 countries where the regulations demand that market milk shall 

 be pasteurised, and in those, such as this country, where milk is 

 expected to be sold in a raw condition. 



Although this test does show roughly whether milk has been 

 previously heated or not, it is not absolutely reliable. The dis- 

 appearance of the colour reaction after the milk has been boiled 

 is somewhat variable and depends upon the length of time of 

 heating, the temperature to which the milk has been raised, and 

 the rate at which the heating has been carried out. These con- 



