326 PHYSIOLOGICAL CHEMISTRY. 



as the one reaction in the intestine in which the presence of bile 

 is actually practically essential, since the old views of the anti- 

 septic value of the bile in preventing excessive intestinal putre- 

 faction have been shown to be without foundation. In a diet 

 rich in fats the emulsifying behavior of the bile unquestionably 

 comes into play as a leading factor in the final absorption. 

 Experiments have been made on animals in which the flow 

 of the bile could be diverted from the natural outlet into the 

 intestine by means of a fistula. In such cases the digestion of 

 proteins and carbohydrates seemed to suffer no change but the 

 digestion of fats was always imperfect and a large portion 

 ultimately escaped with the feces. Indirectly there may be 

 also a loss in protein if the fat in the food in such cases 

 has a rather low melting point and is abundant. A fatty layer 

 encloses portions of the partly digested proteins and prevents 

 access of the digestive fluids until the lower stretches of the in- 

 testine are reached, where bacterial changes soon get the upper 

 hand and rob the protein of any further food value. The 

 action of bile in producing an emulsion with fatty oils may be 

 illustrated by experiment. In an earlier chapter the formation 

 of emulsions by other methods was shown. 



Ex. In a slightly warmed mortar pour about 5 cc. of bile and add to 

 it one cc. of cottonseed oil. Rub the two thoroughly together for several 

 minutes, and then add another small portion of the fatty oil. An emul- 

 sion forms slowly, and becomes more persistent as the working with the 

 pestle is prolonged. The amount of oil which can be brought into the 

 form of a stable emulsion with the 5 cc. of bile depends largely on the 

 character of the oil. The presence of a small amount of free fatty acid 

 in the cottonseed oil aids materially in producing the emulsion. The weak 

 alkalinity of the bile is doubtless an important point here, as through 

 the alkali a little soap is formed and this may be the chief factor in pro- 

 ducing the emulsion. 



Bile contains a large amount of mucin as the analytical 

 table above shows. The stringy character of the secretion is 

 due to this substance which may be recognized by several pre- 

 cipitation tests. The addition of alcohol in excess throws 

 down a flocculent mass which may be separated by the centri- 



