THE CHEMISTRY OF THE DIGESTIVE JUICES 363 



certain adaptation between the food and the digestive secretions. 

 Not the best illustration of this, but one which suits the present topic, 

 is the fact that the food itself probably always contains some free 

 fatty acids when it contains fat at all. Although our knowledge of 

 the mutual action of the pancreatic juice and the bile on the digestion 

 of fats is still incomplete, there is no doubt that they are equally 

 necessary. For in some diseases of the pancreas fat or fatty acid 

 often appears in the stools, and this token of imperfect digestion of 

 the fatty food may be confirmed by the wasting of the patient. The 

 same may occur when the bile is prevented by obstruction of the 

 duct or by a biliary fistula from entering the intestine. Yet in some 

 cases of fistula, where there is every reason to believe that all the bile 

 is escaping externally, the nutrition of the patient at 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 uncommon 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 digestive 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. 408). 



Bile has been credited with a physical power of aiding the passage 

 of fat through membranes moistened with it by diminishing 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 preparation 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 considerably increases 

 the proteolytic power of that secretion (Rachford), although not so 

 decidedly as in the case of the fat-splitting action. The amylolytic 



