BY J. B. HENDERSON, F.I.C.. AND L. A. MESTON. 89 



art' abuornial. particularly in the high proportion of chlorine 

 jjresent. But by far the most striking featui-e of these 

 results is that although the milks vary so far from the normal 

 in chemical composition, the freezing point is practica.lly 

 normal throughout. The mammary glands of the cow, 

 when unable to obtain the correct proportion of milk, 

 sugar and other foodstuffs, adjust the osmotic pressure 

 by adding an extra proportion of common salt from the 

 blood. 



It is evident from the amount of work which has been 

 done l)y many workers in this direction, and the cases 

 quoted give further }>roof. that certain organs of secretion 

 work at definite osmotic pressures. This pressure is 

 practically a constant, the variation being within extremely 

 narrow limits. In the case of milk from the cow, the varia- 

 tion measured by the well known Freezing Point method 

 lies between -0.;")4'C'. and — O.oC^C. This is the first case 

 in many tests where we have found the Freezing Point 

 of an undoubtedly genuine milk to be higher than -0.55°C. 

 Still an extremely rare variation of 0.01 °C. from the normal 

 is not serious in the use of the Freezing Point as a factor 

 in milk analysis. 



It cannot be too strongly impressed on milk analysts 

 that the mammary glands of the cow work almost entirely 

 to a constant osmotic pressure, the constituents which 

 produce the pressure varying according to the nature 

 and amount of the food supply and also according to the 

 period of lactation. 80 far as it is at present known there 

 is no other constant controlling factor. We found exactly 

 the same osmotic pressure (measured by the Freezing 

 Point) in genuine milks which varied bet^^een 6.4 per cent 

 solids not fat with 2.8 per cent fat and 9.7 per cent solids 

 not fat with 5.6 per cent fat. The fact of the osmotic 

 pressui^e being the one steady controlling factor in milk 

 production having been definitely established, it is obviouslj'^ 

 absurd to continiie judging the purity of a milk from the 

 determination of factors which are variant and not con- 

 stants. As the determination of the Freezing Point gives 

 an easy and accurate method of measuring the osmotic 

 pressure, the Freezing Point is obviously the constant 

 factor which should be used in judging the purity of milk. 



G 



