128 MILK AND DAIRY PRODUCTS PART 



certain colouring matters, e.g. indigo-carmine, into the corre- 

 sponding leuco-compound by reduction. He also showed that 

 this property of milk depends upon the micro-organisms which 

 it contains. 



Winter Blyth 1 proved that the same power of reduction is 

 exercised upon litmus, but the application of it as a means of 

 judging the quality of the milk is due to Neisser and Wechs- 

 berg, 2 who proposed the use of methylene blue solution. 

 Afterwards H. Smidt, 3 P. Th. Mliller, 4 and the author, 5 worked 

 further at this method, and showed that there is really a 

 distinct parallel between the number of organisms in the milk 

 and the time required, under certain conditions, for a solution 

 of methylene blue to be decolorised. 



Fresh milk obtained in the usual way requires ten to twelve 

 hours or more for the reduction to be accomplished, whilst a 

 milk that has been badly handled and is very rich in bacteria 

 brings about the decolorisation in a few minutes. 



The test is extraordinarily easy to carry out, and the solution 

 of methylene blue which is used is prepared in the following 

 manner : 



A few grams of methylene blue in powder (the zinc chloride 

 double salt should be used) are digested with about 20 c.c. of 

 alcohol for half an hour at ordinary temperature, and then 5 c.c. 

 of this saturated solution diluted with 195 c.c. distilled water. 

 One c.c. of this solution is then mixed with 10 c.c. of the milk 

 which is to be examined, and a couple of c.c. of paraffin oil 

 floated over it to keep out air, and the whole warmed at 45-50 

 in a water-bath. If the milk becomes colourless within an hour 

 it must be regarded as very bad from a hygienic standpoint, 

 and it is absolutely unsafe for the feeding of young children. 

 When the decolorisation takes place within three hours, the 

 milk may be looked upon as of second quality, whereas if 

 the colour persists for more than three hours the milk is 

 good. 



It must not be concluded that the fermentation and reductase 



Analyst, 1901, Vol. XXVI, p. 148. 

 Miinchener Med. Wochenschrift, 1900, No. 37. 

 Hygienieche Rundschau, 1904, Vol. XIV, p. 1,137. 

 Archivfur Hygiene, 1906, Vol. LVI, p. 108. 



Zeitschrift far Untersuchung cler Nahrwujs- nnd Gennsftmitfel, 1908, 

 Vol. XV, p. 385. 



