138 THE CHEMISTRY OF THE TISSUES AND ORGANS. 



2. This action differs from the action of rennet in the following 

 particulars : 



(a) The precipitate of casein occurs in the warm bath (35-40 C.) 

 in the form of a finely granular precipitate, the milk to the naked eye 

 undergoing no change in its fluidity. On cooling this to the temperature 

 of the air, it sets into a coherent curd which contracts to only a small 

 extent, and is again broken up into fine granules by warming to 35 C., 

 the milk to the naked eye becoming again fluid. This may be repeated 

 a great number of times. 



(b) This phenomenon is not prevented, but only slightly hindered, by 

 such an addition of potassium oxalate as completely inhibits the activity 

 of rennet. 



3. The experiments performed witTi extracts of the gland lead to 

 similar results, which may be masked if the action of the tryptic ferment 

 is very energetic. 



4. The precipitate produced may be provisionally termed pancreatic 

 casein. By the action of rennet it can be converted into true casein. 

 Its solubilities, as summarised in the following table, are partly like 

 those of caseinogen, partly like those of casein. It is probably some- 

 thing intermediate between the two. 



The casein and caseinogen of human milk. The facts described up 

 to the present point are derived from experiments on cows' milk. 

 There are very important differences between this and the principal 

 proteid of human milk. A large number of investigators x have noted 

 such differences as a more finely subdivided and more easily digestible 

 clot formed by rennet, but the difference between the two proteids goes 

 deeper than that. Human caseinogen is more difficult to precipitate by 

 acids (arid is easily soluble in excess) and by salts; it often will not 



1 Bredert and Schroter, Centralbl. f. agric. Chem., Leipzig, 1888; Biedert, " Untersuch. 

 it. d. chem. Unterschiede der Menschen und Kuhmilch," Stuttgart, 1884 ; Langgaard, 

 Virchow's Archiv, Bd. Ixv. ; Makris, Inaug. Diss., Strassburg, 1876. 



