102 DAIRY BACTERIOLOGY 



this will lower the acidity. EllbrecMs titration paper " Exact " 

 has been designed as a colour standard in order to ensure that the 

 same end-point is reached each time. Richmond gives the follow- 

 ing method in his " Dairy Chemistry " : " 10 c.c. of milk are 

 titrated with decinormal baryta, or 11 c.c. with eleventh normal 

 strontia, using 1 c.c. of J per cent, phenol phthalein ; as a standard, 

 an equal volume of milk is coloured with one drop of 0-01 per cent, 

 rosaniline acetate in 96 per cent, alcohol." The degree of acidity of 

 normal milk generally lies between 16 and 19 (6-4 to 7-6 Soxhlet- 

 Henkel). If under 15 (6 S.-H.), the milk is probably derived from 

 cows which are sick or approaching the end of the lactation 

 period, or it may have lost a portion of its natural carbonic acid 

 by having been kept in shallow vessels, shaken or warmed. If the 

 degree of acidity is over 21 (8-4 S.-H.) the milk may be derived 

 from cows suffering from streptococcic mastitis or it may contain 

 colostrum the acidity of which may be as high as 55. As a rule, 

 however, high acidity will be due to incipient lactic acid fermenta- 

 tion. Mixed milk having an acidity of over 21 will usually 

 coagulate on mixing with an equal volume of 68 per cent, alcohol ; 

 this is the basis of the so-called alcohol test. The boiling test is 

 based on the fact that milk having an acidity of over 27-5 coagu- 

 lates on boiling. It is, however, impossible to be certain that the 

 milk will stand pasteurisation if the acidity exceeds 22-5 *. Fresh 

 milk shows an amphoteric reaction towards litmus, i.e., it turns 

 red litmus blue and blue litmus red ; if the degree of acidity is 

 under 12-5, the reaction towards litmus will be alkaline. Accord- 

 ing to Hoyberg 2 , the rosolic acid solution proposed by Hilger for 

 the detection of added soda may be used with advantage in 

 testing milk from the individual quarters with a view to detecting 

 udder disease. If 5 c.c. of 96 per cent, alcohol and 0-5 c.c. of a 

 1 per cent, rosolic acid solution are added to 5 c.c. of milk, an 

 orange colour will be obtained with normal milk, and a red colour 

 with alkaline milk. Eugling 3 has shown that a saturated alcoholic 

 solution of alizarin may be used for the same purpose ; if 5 to 

 10 drops of the solution are added to 50 c.c. of milk, a red-violet 

 colour will be produced with normal milk, a violet-blue colour 

 with alkaline milk, and a yellowish colour with sour milk. Morres 4 

 combines this test with the alcohol test in the Alizarol test, 0-05 per 

 cent, of alizarin being dissolved in the 68 per cent, alcohol, so that 

 an indication may be obtained as to whether the coagulation is 

 due to acid- or rennet-producing bacteria. If narrow test tubes 



1 Henlcel, " Milchwirtschaftliches Zentralblatt," 1907, Bd. III., p. 378. 



"Skandinavsk Veterinaertidsskrift," 1911, p. 23. 



" Handbuch f. die praktische Kaseriei." Leipzig, 1901, p. 20. 

 4 " Oesterreichsche Molkerei-Zeitung," 1912. A colour scale for this 

 test is supplied by Dr. N. Gerbers Co., Zurich. 



