316 ANIMAL PHYSIOLOGY. 
with bacteria. 5. When digestion has proceeded for some time, 
leucin and tyrosin may be shown to be present, though their 
satisfactory separation in crystalline form involves somewhat 
elaborate details. These changes are owing to self-digestion 
of the gland. 
All the properties of this secretion may be demonstrated 
more satisfactorily by making an aqueous or, better, glycerine 
extract of the pancreas of an ox, pig, etc., and carrying on arti- 
ficial digestion, as in the case of a peptic digestion, with fibrin. 
In the case of the digestion of fat, the emulsifying power of a 
watery extract of the gland may be shown by shaking up a 
little melted hog’s lard, olive-oil (each quite fresh, so as to show 
no acid reaction), or soap. Kept under proper conditions, free 
acid, the result of decomposition of the neutral fats or soap 
into free acid, etc.,may be easily shown. The emulsion, though 
allowed to stand long, persists, a fact which is availed of to 
produce more palatable and easily assimilated preparations of 
cod-liver oil, etc., for medicinal use. 
Starch is also converted into sugar with great ease. In 
short, the digestive juice of the pancreas is the most complex 
and complete in its action of the whole series. It is amylolytic, 
proteolytic, and steaptic, and these powers have been attributed 
to three distinct ferments—amylopsin, trypsin, and steapsin. 
Proteid digestion is carried further than by the gastric juice, 
and the quantity of crystalline nitrogenous products formed is 
in inverse proportion to the amount of peptone, from which it 
seems just to infer that part of the original peptone has been 
converted into these bodies, which are found to be abundant or 
not in an artificial digestion, according to the length of time 
it has lasted—the longer it has been under way the more leucin 
and tyrosin present. Leucin is another compound into which 
the amido (NH,) group enters to make amido-caproic acid—one 
of the fatty series—while tyrosin is a very complex member of 
the aromatic series of compounds. Thus complicated are the 
chemical effects of the digestive juices; and it seems highly 
probable that these are only some of the compounds into 
which the proteid is broken up. 
These crystalline bodies may be made artificially by the 
long-continued action under heat of acids and alkalies, in pro- 
teid or gelatinous matter, though it can not be said that these 
facts have as yet thrown much light upon their formation in 
the digestive organs. 
Though putrefactive changes with formation of indol, etc., 
