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 with 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. 
(a) Caseinogen. 
(b) Casein. 
(c) Pancreatic Casein. 
(«) In water + CaC0 3 
Soluble. 
Insoluble. 
Insoluble. 
(b) In lime water . 
Soluble ; precipitable 
Soluble ; precipitable 
Soluble ; precipitable 
with difficulty by 
with ease by CaCL ; 
with ease by CaCL ; 
( !aCl 2 . 
precipitate pro- 
precipitate pro- 
duced by trace of 
duced by trace of 
CaCL at40°, soluble 
CaCl 2 at 40°, not 
on cooling. 
soluble on cooling. 
(c) The precipitate 
Soluble in 5 per cent. 
Insoluble in 5 per 
Slightly soluble in 5 
produced by add- 
NaCl. 
cent. NaCl. 
per cent. NaCl. 
ing CaCL to (b) 
(d) Lime water solu- 
Converted into casein 
So readily precipitable 
Behaves like casein- 
tion. 
by trace of phos- 
by trace of calcium 
ogen. 
phoric acid and 
salts that the action 
rennet. 
of rennet could not 
be properly tested. 
(c) In 0"5 sodium 
Soluble ; precipitable 
Soluble ; precipitable 
Soluble ; precipitable 
bicarbonate solu- 
with ease by CaCL ; 
with difficulty by 
with ease by CaCL ; 
tion. 
precipitate pro- 
CaCL. 
precipitate pro- 
duced by trace of 
duced by trace of 
CaCL at 40°, dis- 
CaCL at 40° C, not 
solves on cooling. 
soluble on cooling. 
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 (and is easily soluble in excess) and by salts ; it often will not 
1 Bredert and Schroter, Centralbl. f. agric. Chem., Leipzig, 1888 ; Biedert, " Untersuch. 
ti. d. chem. Unterschiede der Menschen und Kuhmilcb," Stuttgart, 1884 ; Langgaard, 
Virchoiv's Archiv, Bd. lxv. ; Malms, Inaug. Diss., Strassburg, 1876. 
