Fermentation Test. 219 



residues of starch. Generally only tubes 1 and 2 but sometimes 

 tube 3 become yellow. 



In the presence of large amounts of amylase, which usually 

 runs parallel with the cellular contents, even the other tubes will 

 appear yellow. An increased amount of amylase indicates physio- 

 logical or pathological irritation of the udder. The raw condition 

 of the milk is tested by the determination of peroxydase. There 

 are used either guaiac tinctures, the efficacy of which has been 

 tested, or still better mixtures of guaiac-guaiacol with peroxide of 

 hydrogen, for instance, resina guaiaci 10.0, guaiacol 10.0, 3% 

 perhydrol quantum satis, absolute alcohol 80.0 (Schern). 



Raw milk becomes blue, heated milk turns yellow. The Roth- 

 enfuss reagent is very reliable and is also recommended on account 

 of its keeping qualities. 



First solution : 1 gm. paraphenylendiamin hydrochloride, 15 

 c. c. water. 



Second solution: 2 gm. crystallized guaiacol, 135 c. c. 96% 

 alcohol. 



After dissolving, both are mixed together which results in a 

 white or whitish-yellow reagent. For the execution of the test a 

 0.2% solution of peroxide of hydrogen is also essential. The milk 

 to be tested is mixed with a few drops of a solution of peroxide of 

 hydrogen, and then the reagent is added. Eaw milk at once be- 

 comes intensely violet, while milk heated to over 80 C. remains 

 white. 



The reaction is prettier and more distinct when instead of 

 milk, milk serum is used, which is prepared in the following 

 manner : 



100 c. c. of milk is mixed with 6 to 12 c. c. of lead acetate 

 solution, strongly shaken, and filtered through a folded filter. At 

 the plane of contact of the serum with the reagent, a violet ring 

 appears if the milk is raw. 



If the reaction does not appear, and the lead-acetate-serum 

 becomes turbid through boiling, the milk has been heated above 

 80 C. and probably below the boiling temperature, which however 

 was surely reached when on boiling of the serum no more albumen 

 is precipitated. 



The fermentation test has less importance for the examination 

 of milk to be consumed than of milk to be utilized for the manu- 

 facture of cheese. 



The milk is filled into tall, wide test tubes and the latter are 

 placed for 24 hours in the incubator at 38-40 C. 



Fresh milk does not curdle after 12 hours ; curdled milk should 

 have a pure sour odor and taste, and at the same time a porcelain- 

 like, scaly, coagulum with only a few gas bubbles. Many gas bubbles 

 and fissures in the coagulum indicate the presence of aerogenes-coli 

 and other bacteria which split up the milk sugar with the forma- 

 tion of gas. A cheese-like curd develops as a result of the presence 



