PHYSICAL 



31 



freezing point of milk will never fall below that of blood. He 

 found the freezing point of the blood of the cow to be —0.62° C. 

 and that of cows' milk 0.55° C.±0.06° C. 



In contrast with the relative constancy of the depression of 

 freezing point of cows' milk, the specific conductivity shows 

 greater variations, although milk produced under normal con- 

 ditions does not show very marked differences. 



The following results are given by various observers: 



Table IX 



CONDUCTIVITY OF MILK 



Koeppe (1898) K at 25° C. =0.00430-0.00560 



Lehnert (1897) 0.00487-0.00551 



Schnorf (1905) 0.00485 



Benaghi (1910) 0.00494-0.00517 



Jackson and Rothera (1914) 0.00493-0.00641 



Jackson and Rothera Herd milk (1914) ... =0 . 00549-0 . 00587 



Jackson and Rothera ^^ point out that, owing to the osmotic 

 pressure of milk being controlled by that of the blood, the sub- 

 stances chiefly responsible for this manifestation, viz., the 

 milk sugar and soluble salts, cannot vary independently, but 

 must be inter-related. If the lactose is high the salts must be 

 low, and conversely, if the lactose is low the salts must be high 

 or the osmotic pressure would be lower than normal. Jackson 

 and Rothera found experimentally that the electrical conduc- 

 tivity of milk, which is mainly due to the soluble salts, is in- 

 versely proportional to lactose content. This inverse propor- 

 tionaUty was especially observable in milk produced under 

 pathogenic conditions, as shown by the following example : 



Qxuirter. 



Left anterior (abnormal), 

 Right anterior (normal) . 



Conduc- 

 tivity, K 



0.0114 

 0.00569 



Lactose, 

 Per Cent. 



1.50 

 5.40 



Depres- 

 sion of 

 Freezing- 

 point. A 



0.580 

 0.575 



Sol. Ash, 

 Per Cent. 



0.615 

 0.285 



Insol. Ash, 

 Per Cent. 



0.440 



0.625 



