DIGESTION. 



testine: being pressed on by the contraction of the coats of the gall- 

 bladder, and of the common bile-duct also; for both these organs con- 

 tain unstriped muscular fibre-cells. Their contraction is excited by the 

 stimulus of the food in the duodenum acting so as to produce a reflex 

 movement, the force of which is sufficient to open the orifice of the com- 

 mon bile-duct. 



Bile, as such, is not pre-formed in the blood. As just observed, it is 

 formed or secreted by the hepatic cells, although some of the material 

 may be brought to them almost in the condition for immediate secretion. 

 When it is, however, prevented by an obstruction of some kind, from 

 escaping into the intestine (as by the passage of a gall-stone along the 

 hepatic duct) it is absorbed in great excess into the blood, and, circulat- 

 ing with it, gives rise to the well-known phenomena of jaundice. This 

 is explained by the fact that the pressure of secretion in the ducts is 

 normally very low, and if it exceeds f inch of mercury (16 mm.) the se- 

 cretion ceases to be poured out, and if the opposing force be increased, 

 the bile finds its way into the blood. 



Quantity. Various estimates have been made of the quantity of bile 

 discharged into the intestines in twenty-four hours; the quantity doubt- 

 less varying, like that of the gastric fluid, in proportion to the amount 

 of food taken. A fair average of several computations would give 20 to 

 40 oz. (600-900 cc.) as the quantity daily secreted by man. 



Functions. (1) As an excrementitious substance, the bile may serve 

 especially as a medium for the separation of excess of carbon and hydro- 

 gen from the blood; and its adaptation to this purpose is well illustrated 

 by the peculiarities attending its secretion and disposal ia the foetus. 

 During intra-uterine life, the lungs and the intestinal canal are almost, 

 inactive ; there is no respiration of open air or digestion of food; 

 these are unnecessary, on account of the supply of well elaborated 

 nutriment received by the vessels of the foetus at the placenta. The- 

 liver, during the same time, is proportionately larger than it is after 

 birth, and the secretion of bile is active, although there is no food in the- 

 intestinal canal upon which it can exercise any digestive property. At 

 birth, the intestinal canal is full of thick bile, mixed with intestinal se- 

 cretion; the meconium, or faeces of the foetus, containing all the essential 

 principles of bile. 



Composition of Meconium (Frerichs): 



Biliary resin, 15.6 



Common fat and cholesterin, . . . .15.4 

 Epithelium, mucous, pigment, and salts, . 69.0 



100.0 



In the foetus, therefore, the main purpose of the secretion of bile must 

 }>e the purification of blood by direct excretion, i.e., by separation from 



