152 



EXPERIMENT STATION. 



[Jan. 



Massachusetts Agricultural Experiment Station Herd. 



The results secured and tabulated above justify the following 

 tentative conclusions : — 



1. The serum of a milk of known purity is not likely to have 

 a refractive index below 40. 



2. It seems probable that the refractive index depends, to 

 an extent, upon the stage of lactation of the cow, being highest 

 in the advanced stages, when the animal is giving but little milk. 

 More data are needed, however, to confirm this statement. 



3. Rich milk, containing 4 per cent, or more of fat, has a 

 tendency to give a higher index of refraction than thin milk 

 (less than 4 per cent. fat). This rule, however, does not always 

 hold true. 



4. ]\Iany milks, especially those produced by Jerseys and 

 Guernseys and their grades, can be adulterated with 10 per 

 cent, of water, or 5 per cent, of water and 5 per cent, of skim 

 milk, and escape detection by means of the index of refraction. 

 In case of very rich milk, i.e.; pure milk containing per cent, 

 of fat, it may be possible to add 20 per cent, of water, or 10 per 



