330 PHYSIOLOGICAL DEVELOPMENT. 



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 a mix- 

 ture of these? Modern investigations imply that it is most 

 likely the last. The liver is found to have a compound func- 

 tion. Bernard has proved to the satisfaction of physiologists, 

 that there goes on in it a formation of glycogen a substance 

 which is transformed into sugar before it leaves the liver and 

 is afterwards carried away by the blood to eventually dis- 

 appear in the active organs, chiefly the muscles. It is also 

 shown, experimentally, 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 which results. But while recognizing the fact 

 that the bile consists in part of a solvent, or solvents, aid- 

 ing digestion, there is abundant evidence that one element 

 of it is an effete product; and probably this is the primary 

 element. The yellow-green substance called biliverdine in 

 herbivora and bilirubin in man and carnivora, which gives 

 its colour to bile, is a product the greater part of which is 

 normally cast out from the system continually, as is shown 

 by the contrast between the normal and abnormal colours 

 of faecal matters, and as is still more strikingly shown by 

 the effects on the system when there is a stoppage of the 

 excretion, and an attack of jaundice. Hence we are war- 

 ranted in classing biliverdine as a waste product, and we 



