THE INNER TISSUES OF ANIMALS. 317 



As the mass of bile-cells becomes greater, there arise se- 

 condary lateral cavities opening into the primary one, and 

 through it into the intestine; until eventually these cavities 

 with their coatings of bile-cells, become ramifying ducts dis- 

 tributed through the solid mass we know as a liver. How is 

 this differentiation caused ? 



Before attempting any answer to this question, it is requisite 

 to inquire the nature of bile. Is that which the liver throws 

 into the intestines a waste product of the organic actions ? or 

 is it a secretion aiding digestion ? or is it mixture of these ? 

 Modern investigations imply that it is most likely the last. 

 The liver is found to have a compound function. Bernard 

 has proved to the satisfaction of physiologists, that there goes 

 on in it a formation of glycogen a substance that is trans- 

 formed into sugar before it leaves the liver and is afterwards 

 carried away by the blood to eventually disappear in the lungs. 

 It is also shown, experimentall}', that there are generated in 

 the liver certain biliary acids ; and by the aid either of 

 these or of some other compounds, it is clear that bile 

 renders certain materials more absorbable : its effect on 

 fat is demonstrable out of the body ; and the greatly 

 diminished absorption of fat from the food when the 

 discharge of bile into the intestine is prevented, is probably 

 one of the causes of that pining away that results. But while 

 recognizing the fact that the bile consists in part of a 

 solvent, or solvents, aiding digestion, there is abundant 

 evidence that one element of it is an effete product ; and 

 probably this is the primary element. The yellow-green 

 Bubstance called biliverdine, which gives its colour to bile, is 

 found in the blood before it reaches the liver ; which is not 

 the case with the glycogen or the biliary acids. " As soon as 

 the biliary secretion is in abeyance," says Dr. Harley, the 

 most recent authority on the subject, " biliverdine accumu- 

 lates in the blood (until the serum is as it were completely 

 saturated with the pigment), from which it exudes and stains 

 the tissues, and produces the colour we term jaundice;" 



