456 THE METABOLIC PROCESSES OF THE BODY. 



body in which a similar change of red corpuscles is going on ; it has been 

 suggested that the red marrow of bones is one of these ; but further infor- 

 mation on these points is needed. 



We may then go so far as to say that the bilirubin of the bile is derived 

 from the haemoglobin of the blood, and that the later stages of the trans- 

 formation, including the discharge of the iron of the hsematin component, 

 take place in and by means of the hepatic cell ; but much beyond this is at 

 present uncertain. It must be remembered too that, though after extirpation 

 of the liver no accumulation of bilirubin takes place, showing that the 

 bilirubin is formed by the liver, yet the whole change from red corpuscles 

 to bilirubin may occasionally take place quite apart from the liver, as 

 shown by the presence of hsernatoidin in old blood-clots. 



393. The formation of the bile-acids. About this we know still less. 

 Taking glycocholic and taurocholic acids as the typical bile-acids, recognizing 

 ( 215) that these arise from the union of cholalic acid with glycin and 

 taurin respectively, and remembering that taurin is found in several tissues, 

 and that glycin (see 355) though not an actual constituent of any of the 

 tissues, must certainly arise in tissue metabolism, we may conclude that the 

 chief work in this respect of the hepatic cell is to provide cholalic acid, and 

 to effect the combination with glycin and taurin, though possibly some 

 amount of either one or the other of these bodies may be furnished by the 

 hepatic substance itself. As to how cholalic acid arises out of the metabolism 

 of the hepatic cell, we know no more than we do about the formation of 

 kreatin in muscle or of pepsin in a gastric cell. We are equally ignorant 

 about the origin of glycin and taurin, and cannot explain why in one animal 

 glycocholic and in another taurocholic acid is prominent in the bile, though 

 the two bodies, as shown especially by the presence of sulphur in the taurin, 

 arc widely different. It has been observed that the presence of bile in the 

 intestines seems to excite the liver to increased biliary action j since the bile- 

 acids are rapidly changed in the intestine and the cholalic acid speedily 

 altered, it seems probable that the increased biliary activity is 'due to the 

 absorption of the glycin and taurin respectively. From which we may 

 conclude that the presence of these bodies stirs up the hepatic cell to an in- 

 creased formation of cholalic acid. 



394. As a general rule, the formation of bile-acids runs parallel with 

 the formation of bile-pigment, an increase or decrease of bile meaning an 

 increase or decrease of both constituents. But there are some facts which 

 seem to show that the two actions may be dissociated. The condition or 

 symptom known as "jaundice" is essentially an excess of bilirubin in the 

 blood, whereby the tissues such as the skin and the fluids such as the urine 

 are colored with the yellow pigment. In most of the maladies in which 

 jaundice is a symptom, there is evidence of an obstruction to the flow of 

 bile through the bile passages ; and the presence of bile in the blood, and 

 hence in the tissues at large, is in such cases due to the fact that the bile 

 after secretion by the hepatic cells is reabsorbed from the bile-ducts (see 

 226). 



But in certain cases where jaundice is a prominent symptom, no evidence 

 of any obstruction whatever to the flow of bile can be obtained. This is the 

 case in the jaundice of yellow fever and of a peculiar allied malady known 

 as " acute yellow atrophy of the liver." Now in these cases there is no evi- 

 dence of an accumulation in the blood or elsewhere of bile-acids as there is 

 of bile pigment. And in the obscure malady known as simple or idiopathic 

 jaundice, in which though the anatomical conditions are unknown there is 

 nt least no sign of obstruction, the urine though loaded with bile pigment is 

 said to contain no bile-acids. 



