760 PHYSIOLOGY 



reconverting the latter into glucose and letting it loose into the circulation 

 when this substance is required by the body tissues. In the complete 

 absence of carbohydrate from the food, the liver may, as we shall see later, 

 actually convert the products of protein digestion into sugar. In the same 

 way the liver plays an important part in the metabolism of proteins and 

 of fats, so that its functions will have to be dealt with in the various chapters 

 concerned with the fate of the different foodstuffs and different constituents 

 of the animal body. In this chapter we are merely concerned with its action 

 as a secreting gland. The fact that its secretion is in so many animals 

 poured into the intestine by an orifice common to it and the pancreatic juice 

 suggests that these two fluids co-operate in their actions on the ingested 

 foodstuffs, and points to a direct use of the bile in the processes of digestion. 

 In addition to this function, the bile must also be regarded as an excretion, 

 representing as it does the channel by which the products of disintegration 

 of haemoglobin the red colouring-matter of the blood are got rid of from 

 the organism. As an excretion the production of bile must be continuous 

 and related, not to the processes of digestion, but to the intensity of destruc- 

 tion of the red corpuscles. On the other hand, bile as a digestive fluid is 

 needed in the gut only during the period that digestion is going on. The 

 exigencies of the body therefore require a continuous excretion of bile by the 

 liver, but a discontinuous entry of this fluid into the small intestine. This 

 discontinuity in the entry of a continuous secretion into the intestine is 

 secured, in the majority of animals, by the existence of the gall bladder, a 

 diverticulum from the bile ducts, in which all bile, secreted during the 

 intervals between the periods of digestive activity, is stored up. In the 

 horse, where the gall bladder is absent, its place is taken to some extent by 

 the great size of the bile ducts. Moreover in such an animal the process of 

 digestion is much more continuous in character than it is in carnivora. 

 Since the bile accumulates in the gall bladder during the whole time that 

 digestion is not going on, and is only poured into the gut during digestion, 

 in a fasting animal the gall bladder is distended, whereas in an animal 

 some hours after a meal the gall bladder is practically empty. 



During the period that the bile remains in the gall bladder it under- 

 goes certain changes, as is shown by comparison of the composition of bile 

 obtained from the gall bladder with that obtained from a fistula of the 

 bile duct. 



ANALYSES OF BILE (HUMAN) 



From a biliary fistula (Yco and Herroon) in 100 parts From the gall bladder (Hoppe-Bcyler) in 100 parts 



Mucin and pigments . . 0-148 Mucin . . . . .1-29 



Sodium taurocholato . 0-055 Sodium taurocholatc . . . 0-87 



Sodium glycocholate . 0-165 Sodium glycocholate . . . 3-03 



Cholesterin . .1 Soaps . . . . .1-39 



Lecithin . . 0-038 Cholesterin .... 0-35 



Fats . . . . . J Lecithin 0-53 



Inorganic salts . . 0-slo Fats . . 0-73 

 Water . 98-7 



