340 A MANUAL OF PHYSIOLOGY 



any rate, on a diet not abnormally rich in fat is unaffected. The 

 mere deficiency of bile in the intestine is, of course, complicated 

 in obstructive jaundice by the harmful effects of the biliary 

 constituents circulating in the blood. 



The white stools of jaundice owe their colour, not merely to the 

 absence of bile-pigment, but also to the presence of fat. Their 

 highly offensive odour used to be adduced as evidence that bile is 

 the ' natural antiseptic ' of the intestine. It seems rather to be due 

 to the coating of the particles of food with undigested fat, which 

 shields the proteins from the action of the digestive juices while 

 permitting the putrefactive bacteria to revel in them unchecked. 

 As a matter of fact, the bile itself has little, if any, power of hindering 

 the growth of micro-organisms, although the free bile-acids are 

 tolerably active antiseptics. In suckling children it is not un- 

 common to see the faeces white with fat. This is a less serious 

 symptom than in adults, and perhaps betokens merely that the 

 milk in the feeding-bottle is undiluted cow's milk, which is richer 

 in fat than human milk, and ought to be mixed with water. 



Bidder and Schmidt found that the chyle in the thoracic duct 

 of a normal dog contained 3*2 per cent, of fat. In a dog with 

 the bile-duct ligatured the proportion fell to 0*2 per cent. It is 

 an instance of the extraordinarily exact adaptation of the diges- 

 tive juices to the nature of the food, the mechanism of which will 

 present itself for discussion later on, that the reinforcing action of 

 the bile upon the fat-splitting ferment of the pancreatic juice is 

 said to be greater when the food is rich in fat (p. 381). 



Bile has been credited with a physical power of aiding the 

 passage of fat through membranes moistened with it by diminish- 

 ing the surface tension, and it has been inferred that this has an 

 important bearing on the absorption of fat from the intestine. 

 But the inference does not follow from the statement, and the 

 statement has been itself denied. There is at present no evidence 

 that the digestive function of the bile extends beyond the pre- 

 paration of the food for absorption to the preparation of the 

 mucosa for absorbing it. 



On proteins bile has either no digestive action, or only a feeble 

 one. Fibrin is slightly digested by the bile of the dog and of 

 man. But the addition of it to fresh pancreatic juice consider- 

 ably increases the proteolytic power of that secretion (Rach- 

 ford), although not so decidedly as in the case of the fat-splitting 

 action. The amylolytic action of the pancreatic juice is also 

 favoured by the bile, and in about the same degree as its proteo- 

 lytic effect. Although bile sometimes exerts by itself a feebly 

 amylolytic action, this is not to be included among its specific 

 powers, for a diastatic ferment in small quantities is widely 

 diffused in the body. 



The addition of bile or bile-salts to a gastric digest causes the 



