174 COLLOIDS IN BIOLOGY AND MEDICINE 



through quiet its original viscosity (to within 1 per cent) provided 

 it has not been shaken long enough for curds to form. 



This observation was of great practical importance because milk 

 suffers violent shaking during transportation. Experiments in which 

 milk was carried by wagon, train and post more than three hundred 

 (300) kilometers showed that there was no evident irreversible loss 

 of viscosity. 



Dr. GROSSER, according to a personal unpublished communication, 

 has made a very noteworthy observation in the ultrafiltration of 

 milk. 1 It was shown that raw milk gave an ultrafiltrate much 

 richer in lime than did boiled milk. In boiling, the calcium is bound 

 to the milk colloid and remains with the latter on the ultra-filter. 

 Thus, a simple means is furnished for distinguishing raw from cooked 

 milk. Definite differences exist between human and cow's milk 

 which offer a new basis for the difference these two kinds of milk 

 exhibit in respect to their assimilibility (available food value). 



The classification of the milk colloids to which J. ALEXANDER and 

 J. G. M. BULLOWA have drawn attention must be considered in 

 future tests of milk (see p. 349). 



Since the water and the crystalloid content of milk are almost con- 

 stant, many adulterants can be detected by the departure of the 

 water and the milk content from the normal. For this purpose it is 

 necessary to remove the fat and colloid constituents without chang- 

 ing the content in water and salts. To determine the addition of 

 water, J. MAI and S. ROTHENFUSSER* coagulate the milk colloids with 

 calcium chlorid and then measure the water content by refraction. 

 KURT OPPENHEIMER determines the milk sugar polarimetrically, after 

 he has removed the milk colloids with colloidal ferric hydroxid. 

 According to S. ROTHENFUSSER, by treating milk with lead acetate 

 in strong ammoniacal solution at 85 C., the milk sugar is adsorbed 

 when the colloids are coagulated, while saccharose remains in solu- 

 tion. According to ROTHENFUSSER,* the smallest adulteration with 

 foreign sugar (saccharated lime) may thus be detected. 



Among dairy products, condensed milk must be considered as of 

 great importance. This is milk which is evaporated with the addition 

 of 25 to 50 per cent cane sugar. All who are forced to use it, es- 

 pecially colonists, know how ill it satisfies the demand for a milk 

 substitute. One of the essential properties of colloids is that their 

 condition is not reversible to the same extent as crystalloids. This 

 may be, in addition to the destruction of certain flavoring substances, 

 an important reason for the lessened value of condensed milk. The 

 various dried milk products when stirred with cold or warm water 

 1 In a private communication, as yet unpublished. 



