56 THE NORMAL COMPOSITION OF MILK 



stances or by the abstraction of the natural constituents, gen- 

 erally by human agency, is usually conveyed by the term milk 

 adulteration, and this, strictly speaking, has no reference to 

 any standard that may be adopted. 



For the detection of adulteration, a complete determination 

 of the various constituents of the sample should be made and the 

 amounts of fat, lactose, proteid, and ash so found compared 

 with the percentages as calculated from the formula of Van 



j - i, j rm. proteid , lactose 



Slyke, Olsen, and Richmond. The . - and ratios 



fat proteid 



should also be calculated. The addition of water does not 

 give proteid values which are materially different from those 

 calculated by the Olsen formula but are invariably less than 

 those calculated by the Van Slyke formula, the difference being 

 proportional to the amount of water added. The PVS (proteid 

 calculated by the Van Slyke method) in this case, is greater 

 than the P. 0. (proteid calculated by the Olsen method). The 



,,.,. r ,, proteid , lactose ,. 



addition of water leaves the , . - and ^ ratios un- 



fat proteid 



changed. 



The amount of proteid found by direct estimation in the 

 case of abstraction of fat would be greater than either of the 

 calculated values, and in this case P.O. would be greater than 

 PVS. This is due to the Van Slyke formula being based on the 



constituent which has been abstracted. The -^ ratio 



proteid 



would be normal and the pr ^ ratio abnormally high. In 



lat 



both of these instances the r-: ratio is unaltered and this 



proteid 



is valuable in distinguishing between naturally abnormal milks 

 and those rendered abnormal by external agencies. High 



r-:- ratios are extremely rare but low ones may be pro- 



proteid 



duced by the various causes previously mentioned. 



The refractive power of the serum should also be considered 



