BY ti. S. HALCRO WARDLAW. 62l 



conductivity of milk by examining the relation l)et\veen this 

 effect and the number of fat-globules in a given volume of fat. 



The effect of non-conducting suspended matter on the con- 

 ductivity of electrolytes has been studied by Oker-Blom (11)00). 

 He determined the conductivity of suspensions of sand in jellies 

 made up with salt solutions, and came to the conclusion that the 

 size of the particles (between 2 and under 05 mm.) made no 

 difference to their effect on the conductivity, but that the sand 

 depressed the conductivity less when uniformly distributed 

 through the jelly than when collected into one layer. These 

 conclusions are to a certain extent contradictory, however, as 

 the difference between the first and second cases is mainlv 

 one of aggregation. Further, the range of size of particles ex- 

 amined in the first case was not very great. 



The sizes of the fat-particles even in one sample of milk vary 

 enormously. But each sample contains a certain average size and 

 number of particles in a given volume, and well-defined diff'er- 

 ences exist between the sizes and numbers for samples of different 

 origin, ^trippings, for instance, contain larger fat-globules than 

 first milk, and the milk of Jersey cows contains larger particles 

 than the poorer milk of Shorthorn cows. 



The number of fat-globules in the milk was counted Vjy the 

 method of Babcock (1886) as modified by Shaw and Eckles 

 (1909). One volume of milk is diluted to 50 with water. The 

 mixture is drawn up into capillary tubes, the internal diameters 

 of the tubes are measured, and the numbers of globules in a 

 known length are counted. From the figures obtained, the 

 numbers of globules in a known volume of the undiluted milk 

 may be calculated. The measurements are made with an ocular 

 micrometer. The workers quoted made the optic measui-ements 

 with the capillaries immersed in glycerine. It was found in the 

 present work, however, that owing to the differences between 

 the refractive index of glycerine and that of glass, the values of 

 the diameter of the capillaries measured in this wa}- were too 

 high. The present measurements, therefore, were made with 

 the tubes immersed in a solution of chloral hydrate in glycerine 

 (7:1). This solution has a refractive index of 1'508, which is 



