506 DIGESTION. 



times falls, but as the vena cava and other parts are generally 

 compressed likewise, the result is not constant. To show ab- 

 sorption from increased pressure in the ducts, replace the water 

 in the manometer by aqueous solution of indigo-carmine, taking 

 care that the column of fluid stands several inches above the 

 highest level previously attained by it. The solution is gradu- 

 ally absorbed, muscular tremors occur, and the animal dies 

 just as if water had been injected into the veins. At the same 

 time the surface becomes colored blue by the indigo-carmine. 

 The experiment enables us to understand how a very slight 

 obstruction to the orifice of the bile duct is sufficient to deter- 

 mine re-absorption, and the production of jaundice. 



GLYCOGEN. 



153. It would form a marked exception to the economical 

 use of material which we find in the body if the liver, the 

 largest gland in it, had as its sole function the secretion of 

 bile; a fluid of much less importance in digestion than the 

 gastric or pancreatic juices. This, however, is not the case, 

 for, in addition to secreting bile, the liver has the power of 

 forming glycogen, a substance winch resembles dextrin in its 

 reactions, and like it, can be converted into sugar by the action 

 of ferments. It is always present in the liver in larger amount 

 during digestion than during fasting. What the materials 

 from which it is formed actually are is uncertain. Its amount 

 is increased by the use of starchy food ; but as it continues to 

 be formed in considerable quantity when the food consists of 

 flesh alone, it is evident that it can be produced from albumin- 

 ous bodies. In support of its origin from albumin, it has 

 been argued .that the increased amount which is met with after 

 the administration of starchy food, is due to the sugar derived 

 from the starch being burnt off instead of albumin, in con- 

 sequence of which more albumin remains to be converted into 

 glycogen. The experiments of Cyon (if the}'' are to be relied 

 upon) make it probable that urea is formed in the liver. As 

 the amounts of sugar and urea excreted by diabetic patients 

 fed on an nnimal diet, run parallel with one another, it might 

 be supposed that when the diet is exclusively albuminous, 

 glycogen is formed by albumin or peptones splitting up and 

 yielding glycogen and urea. Again, when the diet consists of 

 starch and sugar, glycogen is formed abundantly, and at the 

 same time a deposit of fat takes place in the liver. From this 

 it might be supposed that the sugar absorbed from the intes- 

 tine is decomposed so as to yield glycogen and fat. Glycogen 

 seems to be of great importance for cell growth, for it is found, 

 wherever this is going on actively, as in new formations, or in 

 embryonic tissues. A remarkable experiment of Hoppe-Seyler 



