714 PHYSIOLOGY 



the latter into glucose and letting it loose into the circulation when this sub- 

 stance is required by the body tissues. In the complete absence of carbo- 

 hydrate 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 food-stuffs 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 food- stuffs, 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 ex- 

 cretion the production of bile must be continuous, and related, not to the 

 processes of digestion, but to the intensity of destruction 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 (Yeo and Herroun) in From the gall-bladder (Hoppe-Seyler) in 



100 parts 100 parts 



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



Sodium taurocholate . . 0-055 Sodium taurocholate . .0-87 



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



Cholesterin . ~\ Soaps 1-39 



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



Fats Lecithin . . . . .0-53 



Inorganic salts . . . 0-840 Fats . . . . .0-73 

 Water 98-7 



