156 DIGESTION. 



effect is instantaneous and permanent, and only requires that the 

 two substances be well mixed by gentle agitation. It is singular 

 that some of the German observers should deny that the pancreatic 

 juice possesses the property of emulsioning fat, to a greater extent 

 than the bile and some other digestive fluids ; and should state that 

 although, when shaken up with oil, outside the body, it reduces 

 the oily particles to a state of extreme minuteness, the emulsion 

 is not permanent, and the oily particles "soon separate again on 

 the surface." 1 We have frequently repeated this experiment with 

 different specimens of pancreatic juice obtained from the dog, and 

 have never failed to see that the emulsion produced by it is by 

 far more prompt and complete than that which takes place with 

 saliva, gastric juice, or bile. The effect produced by these fluids is 

 in fact altogether insignificant, in comparison with the prompt and 

 energetic action exerted by the pancreatic juice. The emulsion 

 produced with the latter secretion may be kept, furthermore, for at 

 least twenty-four hours, according to our observations, without any 

 appreciable separation of the oily particles, or a return to their 

 original condition. 



The pancreatic juice, therefore, is peculiar in its action on oily 

 substances, and reduces them at once to the condition of an emul- 

 sion. The oil, in this process, does not suffer any chemical.ujyLera- 

 tion. It is not decomposed or saponified, to any appreciable extent. 

 It is simply emulsioned ; that is; it is broken up into a state of minute 

 subdivision, and retained in suspension, by contact with the organic 

 matter of the pancreatic juice. That its chemical condition is not 

 altered is shown by the fact that it is still soluble in ether, which 

 will withdraw the greater part of the fat from a mixture of oil and 

 pancreatic juice, as well as from the chyle in the interior of the 

 intestine. In a state of emulsion, the fat, furthermore, is capable 

 of being absorbed, and its digestion may be then said to be accom- 

 plished. 



We find, then, that the digestion of the food is not a simple 

 operation, but is made up of several different processes, which 

 commence successively in different portions of the alimentary 

 canal. In the first place, the food is subjected in the mouth to the 

 physical operations of mastication arid insalivation. Reduced to a 

 soft pulp and mixed abundantly with the saliva, it passes, secondly, 

 into the stomach. Here it excites the secretion of the gastric juice, 



1 Lehmann's Physiological Chemistry. Philada. ed., vol. i. p. 507. 



