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THE RELATION BETWEEN THE FAT-CONTENT AND 

 THE ELECTRICAL CONDUCTIVITY OF MILK. 



By H. S. Halcro Wardlaw, D.Sc, Linxean Macleay Fellow 

 OF THE Society in Physiology. 



(From the Physioloyical Laboratory of tJie University of Sydney.) 



Milk consists of water containing substances in solution, in 

 the colloidal state, and in suspension. The electrical conduc- 

 tivity of milk is due to the presence of ionised salts among the 

 substances in solution. The colloidal and the suspended matter, 

 the protein and the fat, do not contribute appreciably to the 

 transport of electricity. These substances, in fact, depress the 

 conductivity, for they displace a certain amount of conducting 

 material. 



The eftect of protein on the conductivity of milk has been 

 studied bv Jackson and Rothera (1913). They removed the 

 proteins from separated milk by dialysis, and found that each 

 gram of protein in 100 cc. of the separated milk depressed the 

 electrical conductivity by 2 •76%. 



The effect of fat on the conductivity is shown by the figures 

 given by Taylor (1913). He found, as an average of five ex- 

 periments, that the removal of 5% of fat from milk caused an 

 increase of electrical conductivity of 11 4%. This increase of 

 conductivity is more than twice as great as that which would be 

 accounted for by the increased concentration of electrolyte due 

 to the removal of the fat. The excess is ascribed by Taylor to 

 the removal of the mechanical obstruction which the fat-globules 

 may offer to the movement of the ions. 



The object of the present work was to investigate more closely 

 the relation between the fat-content of cows' milk and its elec- 

 trical conductivity. 



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