306 COMPARATIVE PHYSIOLOGY. 



use of a trace of copper sulphate added to a few drops of caustic 

 alkali, which becomes red if this body be present. 4. After a 

 few hours the smell becomes faecal, owing in part to indol, 

 which gives a violet color with chlorine-water; while under 

 the microscope the digesting mass may be seen to be swarming 

 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, glycerin 

 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, tripsin, 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 (NHa) 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 eflFects of the digestive juices ; and it seems highly 

 probable that these are only some of the compounds into which 

 the proteid is broken up. Though putrefactive changes with 



