SECRETION AND EXCRETION 



349 



were removed by means of colloidal iron oxid), against whey (the 

 casein was removed by rennin) and against distilled water. Whole 

 milk contained approximately about 0.15 per cent CaO; iron- 

 milk about 0.12 per cent CaO; and whey only from 0.04 to 0.06 per 

 cent CaO. The amount of diffusible lime is accordingly only about 

 0.06 to 0.07 per cent CaO and consists thus of about 40 to 50 per 

 cent of the entire lime contained. 



It is remarkable that the iron-milk contains more lime than is 

 really diffusible, so that when casein is flocked out by colloidal iron 

 oxid, calcium goes into true solution. But the iron-whey contains 

 much less phosphoric acid than the milk so that it must have been 

 precipitated by the iron oxid. From this it is evident that no 

 considerable quantity of calcium phosphate is in colloidal solution 

 or the lime would be retained with the phosphoric acid by colloidal 

 iron oxid. Evidently the lime exists to a considerable extent in 

 solution as a slightly dissociated casein salt. In favor of this view 

 are the other properties of milk, which are manifested when the equi- 

 librium is shifted (depression of freezing point, conductivity) . 



Albumin. The milk of various animals varies much in the pro- 

 portionate amounts of the chief constituents; especially contrasted 

 is the relation between casein and albumin, as the following data 

 show: 



The significance of these differences upon the structure of the 

 different organisms cannot be determined at present, though ac- 

 cording to the investigations of J. ALEXANDER and J. G. M. BUL- 

 LOWA,* the digestibility is influenced by this ratio. These investi- 

 gators are of the opinion that the reversible albumin serves as a 

 protective colloid for the irreversible casein. They base this on the 

 fact that woman's milk, which is rich in albumin, is difficult to 

 coagulate by acids or rennet, and that the same condition obtains 

 for cow's milk if it is protected by gelatin, gum arabic, albumin or 

 the like. 



In the dark field, too, human milk shows a finer division than 

 cows' milk, as was shown by the investigations of J. LEMANISSIEE,* 

 A. KREIDL and NEUMANN,* as well as G. WIEGNER.* Two distinct 



