396 HANDBOOK OF PHtSIOLOGY. 



xtone blocking the hepatic duct, it is reabsorbed in great excess into 

 the blood, and, circulating with it, gives rise to the well-known phenom- 

 ena of jaundice. This is explained by the fact that the pressure of 

 secretion in the ducts although normally very low, not exceeding 15 

 mm. in the dog, is still higher than that of the portal veins, and if it 

 exceeds 16 mm. the secretion although formed ceases to be poured out, 

 and if the opposing force be increased, the bile passes into the blood- 

 vessels through the lymphatics, and the yellow color appears in the skin 

 and in the secretions, and constitutes the condition of jaundice. In 

 jaundice the faeces are light colored and highly offensive, there is con- 

 stipation, the heart beats slowly, and from the presence of bile salts as 

 well as bile pigment in the blood, the red blood corpuscles may be in 

 part dissolved. The latter action results in the presence of hemoglobin 

 and of an additional amount of bile pigment in the urine. 



Disposal of the Bile. The simple excretion of the foetal bile makes 

 it probable that the bile in extra-uterine life is also, at least in part, des- 

 tined to be discharged as excrementitious. The analysis of the faeces 

 shows, however, that (except when rapidly discharged in purgation) they 

 contain very little of the bile secreted, probably not more than one-six- 

 teenth part of its weight, and that this portion includes chiefly its col- 

 oring matter in the form of stercobilin, and some of its fatty matters 

 and mucin, but its salts to only a very slight degree, almost all of which 

 have been reabsorbed from the intestines into the blood. The bilirubin 

 is in part converted into urobilin and is reabsorbed and excreted by the 

 kidneys in the urine. 



The elementary composition of bile-salts shows such a preponderance 

 of carbon and hydrogen that probably, after absorption, they combine 

 with oxygen, and are excreted in the form of carbonic acid and water. 

 The change after birth, from the direct to the indirect mode of excre- 

 tion of the bile may, with much probability, be connected with a purpose 

 in relation to the development of heat. The temperature of the foetus 

 is largely maintained by that of the parent, but, in extra-uterine life, 

 there is (as one may say) a waste of material for heat when any excre- 

 tion is discharged unoxidized; the carbon and hydrogen of bilin, there- 

 fore, instead of being ejected in the faeces, to a very large extent (viz., 

 f ), are reabsorbed, in order that they may be combined with oxygen, and 

 that in the combination heat may be generated. It appears that tauro- 

 cholic acid may easily be split up in the intestine into taurin and chola- 

 lic acid, and the same is probable of glycocholic acid. Taurin, glycin, 

 and cholalic acid have all been detected in small amounts in the faeces. 

 So that the bile is in part excreted, but in part is reabsorbed from the 

 intestine (chiefly the large), and returned to the liver. What may be 

 the ultimate destination of these altered or unaltered constituents is un- 

 known. Glycin is supposed to go partly to form urea, and taurin is ex- 



