176 DIGESTION. 



especially distinguished from the other digestive secretions. If a fluid 

 fatty substance, such as olive oil or melted butter, be shaken up in a 

 test-tube with the saliva, the gastric juice, the bile, or any of the 

 excreted fluids, it suffers no change in its physical characters. It is 

 partially broken up by the mechanical agitation, but, on being allowed 

 to remain at rest, the oil globules run together and soon collect in a 

 distinct layer upon the surface of the liquid. If, on the contrary, the' 

 same experiment be tried with fresh pancreatic juice, the oil is instantly 

 broken up into a state of fine subdivision, producing a uniformly white, 

 opaque, milky looking fluid. The emulsion thus formed is permanent, 

 the microscopic fat granules being held in suspension by the organic 

 matter of the secretion, and thus prevented from uniting into visible oil 

 drops. If the proportion of oily matter be considerable, a part of it may 

 rise to the surface as a creamy layer, and if it be in excess, the super- 

 fluous portion will also rise to the upper part of the liquid ; but the 

 remainder will continue indefinitely in the emulsioned condition, dis- 

 seminated uniformly through the fluid mixture. 



The emulsifying property of the pancreatic juice is very active, when 

 the secretion exhibits its normal characters. Bernard found that the 

 freshly extracted j uice formed a complete emulsion at 38 (100 F.) with 

 olive oil, butter, suet, or lard, when mixed with either of these substances 

 in the proportion of one gramme of oleaginous matter to two grammes 

 of pancreatic juice. The emulsion thus produced retained its physical 

 appearance unchanged, although allowed to remain at the above tempe- 

 rature for fifteen or eighteen hours. 



The power of the pancreatic juice to emulsify oils, though facilitated 

 by its alkaline reaction, does not depend upon the free alkali, but is 

 mainly due to the action of its organic matter. This is indicated by the 

 fact that other animal fluids which are also alkaline do not have the 

 same power in a corresponding degree ; and Bernard has shown that the 

 pancreatic juice, after being neutralized by a dilute acid, still retains its 

 property of acting upon the fats. 



The property of emulsifying oily matters, first shown to exist in the 

 pancreatic juice of the dog, has been found by Colin in that of the 

 horse, the ass, the ox, the sheep, and the pig; and by Bernard has been 

 found fully developed in that of the goose. According to Colin, its 

 intensity, in these different animals, is proportional to the quantity of 

 albuminous matter contained in the secretion ; one part of oil requiring, 

 for complete emulsion, from two to three parts of pancreatic juice 

 when its albuminous ingredient is abundant, and four, five, or six parts 

 when the proportion of this substance is diminished. 



There is every evidence that the emulsifying action of the pancreatic 

 juice is of the first importance in the digestion of fatty substances. 

 These substances are not affected by contact with gastric juice outside 

 the body ; and examination shows that they are not digested .in the 

 stomach, but are unchanged in their essential character so long as they 

 remain in the gastric cavity. They are merely melted by the warmth 



