344 HUMAN PHYSIOLOGY 



Nucleo-proteid and Mucin. The bile owes its viscosity to 

 the presence of a mucin-like body, which, however, does not 

 yield sugar on boiling with an acid and which contains phos- 

 phorus. It is precipitated by acetic acid, but is soluble in 

 excess. It is therefore a nucleo-proteid. In some animals 

 a certain amount of mucin is also present. (Chemical 

 Physiology, p. 21.) 



Inorganic Constituents. The most abundant salt is phos- 

 phate of calcium. Phosphate of iron is present in traces. 

 Carbonate of soda and of calcium and chloride of sodium are 

 the other chief salts. 



2. Flow of Bile. The bile, when secreted by the liver 

 cells, may accumulate in the bile passages and gall bladder 

 to be expelled under the influence of the contraction of the 

 muscles of the ducts or of the pressure of the abdominal 

 muscles upon the liver. The flow of bile into the intestines 

 thus depends upon 1st, The secretion of bile; 2nd, the 

 expulsion of bile from the bile passages. It is exceedingly 

 difficult to separate the action of these two factors. The flow 

 of bile in the human subject has now been studied in several 

 cases in which the surgeon has had to make a fistula into 

 the gall bladder through which all the bile secreted escaped 

 and could be collected. 



The flow of bile begins in intra-uterine life before the 

 twelfth week, and it continues without intermission through- 

 out the whole of life, even during very prolonged fasts. The 

 taking of food increases the flow of bile, and the extent to 

 which it is increased depends largely on the kind of food 

 taken. In the dog a proteid meal has the most marked 

 effect, a fatty meal a less marked effect, and a carbohydrate 

 meal hardly any effect. The increased flow of bile following 

 the taking of food does not reach its maximum till six or 

 nine hours after the food is taken, and some observers have 

 found that the period of maximum flow is even further pro- 

 longed. Very often, immediately after food is taken, there 

 is a markedly increased flow due to the stimulation of the 

 muscles of the bile passages, but the later increase seems to 

 be due to a true increased formation of bile. When the indi- 

 vidual is taking a liberal diet the secretion of bile appears to 



