334 DIGESTION. 



also, at least in part, destined to be discharged as 

 excrementitious. But the analysis of the fseces of both 

 children and adults shows that (except when rapidly dis- 

 charged in purgation) they contain very little of the bile 

 secreted, probably not more than one-sixteenth part of its 

 weight, and that this portion includes only its colouring, 

 and some of its fatty matters, but none of its essential 

 principle, the bilin. All the bilin is again absorbed from 

 the intestines into the blood. But the elementary compo- 

 sition of bilin (see p. 331) shows such a preponderance of 

 carbon and hydrogen, that it cannot be appropriated to 

 the nutrition of the tissues ; therefore, it may be presumed 

 that after absorption, the carbon and hydrogen of the 

 bilin combining with oxygen, are excreted as carbonic 

 acid and water. The destination of the bile is, on this 

 theory, essentially the same in both foetal and extra- 

 uterine life ; only, in the former, it is directly excreted, in 

 the latter indirectly, being, before final ejection, modified 

 in its absorption from the intestines, and mingled with the 

 blood. 



The change from the direct to the indirect mode of 

 excretion of the bile may, with much probability, be con- 

 nected with a purpose in relation to the development of 

 heat. The temperature of the foetus is maintained by that 

 of the parent, and needs no source of heat within the 

 body of the foetus itself ; but, in extra-uterine life, there is 

 (as one may say) a waste of material for heat when any 

 excretion is discharged unoxidized ; the carbon and hydro- 

 gen of the bilin, therefore, instead of being ejected in the 

 fseces, are re-absorbed, in order that they may be com- 

 bined with oxygen, and that in the combination, heat may 

 be generated. 



From the peculiar manner in which the liver is supplied 

 with much of the blood that flows through it, it is probable, 

 as Dr. Budd suggests, that this organ is excretory, not 

 only for such hydro -carbonaceous matters as may need 



