ACTION OF THE ENZYMES. 113 



inogen and casein be taken to indicate that they are not the 

 same chemically, for all the stated differences can easily be 

 explained on the assumption that the two represent physical 

 modifications of one and the same substance. 



As stated above, calcium salts are not the only ones 

 to bring about a precipitation of casein. At the proper 

 concentration a large number of salts cause the precipitation 

 not only of casein but of caseinogen as well. Arranged in 

 the order of their effectiveness the salts of the different 

 metals read as follows: 



(1) Metals which precipitate neither casein nor caseinogen: 

 Sodium, potassium, ammonium, rubidium (?), caBsium (?). 



(2) Metals which at room temperature quickly precipi- 

 tate casein, but caseinogen only after remaining at 40 C. 

 for some time or on heating to a still higher temperature: 

 Lithium, beryllium, magnesium, calcium, strontium, barium, 

 manganese (ous), iron (ous), cobalt (ous), nickel (ous). 



(3) Metals which precipitate both casein and caseinogen 

 at room temperature: The remaining heavy metals, includ- 

 ing iron (ic). 



As we pass from the first group through the second to 

 the third, the precipitating power of the metals for both 

 casein and caseinogen increases progressively. 1 



1 See OSBORNB: Journal of Physiology, 1901, XX VII, p. 398; CON- 

 RADI: Miinchener medizinalische Wochenschr. XL VIII, 1901, (1), p. 175; 

 LOEVENHART: Zeitschrift fur physiologische Chemie, 1904, XLI, p. 177. 



