138 PHYSIOLOGY CHAP. 



secretion, which commences suddenly, reaches its maximum at the 

 third hour, and ceases entirely during the sixth hour. 



After a mixed meal the increase may be marked, when proteins 

 and fats predominate (see diagram), or slight, as when the carbo- 

 hydrates predominate. 



These striking results, along with what is known of the 

 metabolism of the hepatic cells, suggest interesting considerations, 

 which we shall discuss in a future chapter, in studying the liver 

 as an organ of internal secretion. Here we must confine ourselves 

 to stating that the formation of bile is not activated by the 

 presence of food-stuffs in the gastro-intestiual tube, as a reflex 

 along nerve paths, but only when the alimentary substances 

 reach the liver by way of the portal vein, after digestion and 

 absorption. In fact, the experiments of Barbera show that the 

 influence of the food on bile secretion is conditioned by digestion 

 and absorption. When injected per rectum, those food-stuffs only 

 increase the secretion of bile which are absorbed (carbohydrates 

 and proteins), not such as are non-absorbable by this method 

 (fats). 



The production of bile continues to a less extent, even when 

 the products of food digestion no longer reach the liver. During 

 a fast protracted till death occurs from inanition (Chossat, Luciani, 

 Albertoni), the amount of bile secreted gradually diminishes, 

 but is not arrested, up to the end. Albertoni, who studied 

 this phenomenon methodically (1893), saw that in fasting the 

 quantity of bile secreted diminished daily, while its specific gravity, 

 i.e. the relative amount of solid residues, nitrogen, and sulphur, 

 increased. 



Bile is also formed from the third month of intra-uterine life, 

 and during the lethargic period of hibernating animals, though 

 only in small quantities (as in the fasting state). 



According to Brand (1902), who studied the secretion and 

 composition of human bile in nine cases of fistula of the gall- 

 bladder, the amount of bile that flows out in man (from a complete 

 fistula) varies considerably from hour to hour. The daily amount 

 oscillates between 500 and 1100 c.c. The biliary secretion dimin- 

 ishes in the night, and falls to its minimum in the early hours of 

 the morning ; it then increases rapidly, reaches its maximum 

 about noon, and is usually succeeded by another maximum in the 

 evening. G. Galli (1906) obtained similar results in an analogous 

 case of fistula of the gall-bladder in a woman. 



This proves that the secretion of bile, unlike the other secretions 

 which we have previously studied, is not co-ordinated with the 

 digestion of foods, since it is effected under conditions in which no 

 digestion takes place in the intestine, and increases when digestion 

 and absorption have already occurred. Biligenic and cholagogic 

 materials, such, i.e., as are capable of being transformed in the liver 



