THE BIOCHEMICAL PROCESSES OF DIGESTION 531 



pleural and peritoneal cavities. The endothelial cells of the blood vessels 

 and elsewhere can evidently form the pigments, at least when the liver is 

 absent. When such a process occurs under normal conditions, it is quite 

 probable that the liver acts merely as an excretory organ for the pig- 

 ments in the same way as the kidney does for urea. Possessed of endo- 

 thelial cells, the liver might itself also produce some of the pigments, 

 but no more than other organs with a similar number of those cells. 



The derivation of bile pigments directly from hemoglobin is not their 

 only source, for the same workers have observed that, whereas the excre- 

 tion of pigment from a biliary fistula is remarkably constant in a dog 

 fed on a fixed mixed diet, it became increased, sometimes by 100 per 

 cent, when the diet was changed to one of carbohydrates, and depressed 

 on a diet of meat. The question arises as to whether all of the bile 

 pigments are really derived from broken-down hemoglobin. May they 

 not also be manufactured de novo out of other materials'? 



Whipple and Hooper have also shown that bile is a most important 

 secretion, for dogs rarely survive on an ordinary diet if bile is perma- 

 nently prevented from entering the intestine. Intestinal symptoms 

 soon supervene, and become progressively more severe until the death 

 of the animal. Feeding with bile does not relieve the condition, but 

 feeding with cookedjiver seems to have a beneficial effect. 



Bile salts and pigments usually accompany each other when any- 

 thing occurs to interfere with the free secretion of bile. For example, 

 after ligation of the bile duct both bile pigments and bile salts accumu- 

 late in the blood, in the serum of which they may be recognized by the 

 ordinary chemical tests in from four to six hours after the operation. 

 If the accumulation be allowed to proceed further, the bile pigments 

 become deposited in the tissues, giving them the peculiar yellowish ap- 

 pearance known as jaundice. Under these conditions the bile salts and 

 pigments also appear in the urine. The accumulation of bile salts in 

 the body affects certain physiological processes; for one thing, it causes 

 a great lengthening in the clotting time of the blood. 



If the blood supply to the liver is interrupted by ligation of the portal 

 vein and hepatic artery at the same time that the bile ducts are occluded, 

 not a trace either of bile salts or of bile pigment appears in the blood 

 during the six to eighteen hours that the animals survive the operation. 



The amount of obstruction of the bile duct necessary to produce these 

 symptoms is very slight, since bile is secreted at a very low pressure. 

 Even a clot of mucus or a swollen condition of the mucous membrane 

 of the duct is sufficient to produce obstruction. In the discharge of bile 

 from the gall bladder into the duodenum it is claimed by Meltzer 26 that a 

 reciprocal relationship exists between the contraction of the bladder 



