For most practical purposes the bile from the gall bladder of recently killed animals is sufficient. The bile pigments and cholesterin may be conveniently obtained from the gall stones so often found in the human gall bladder.

In order to investigate the composition of the bile as it comes from the ducts, before it has been modified by its sojourn in the gall bladder, it is necessary to make a biliary fistula, communicating either with the gall bladder or with the bile duct. In this way the rate, pressure, and other points concerning the mode of secretion may be determined.