448 A TEXTBOOK OF PHYSIOLOGY 



muscles (see p. 427). The liver probably also forms glycogen from 

 other bodies, including the non-nitrogenous moiety left over when 

 certain amino-acids are deaminized, either in the intestinal mucous 

 membrane or in the liver itself (cf. p. 424). 



3. Storage of Fat. Although the liver contains a certain per- 

 centage of " masked " fat that is, fat which is not visible to staining 

 processes under certain circumstances, such as during pregnancy 

 and lactation, the liver contains large amounts of visible fat, the 

 exact significance of which is not known. Thus visible fat in the 

 liver, which occurs in " fatty degeneration," is not always a patho- 

 logical phenomenon. 



4. The Formation of Uric Acid. The liver possesses deaminizing 

 enzymes which are capable of converting purin bodies, such as adenin 

 and guanin, into the oxypurins hypoxanthin and xanthin, and also 

 oxidizing enzymes capable of converting these bodies to uric acid. 

 It also in the mammal contains a uricolytic enzyme which turns uric 

 acid into urea. 



5. The Formation of Urea. The liver plays an important part in 

 the metabolism of protein, particularly in the end processes of this 

 metabolism which result in the formation of urea. 



The fact that urea is formed in the liver can be demonstrated in 

 various ways : 



(1) Extirpation of the liver in the frog leads to a diminution in 

 the amount of urea excreted, and an increase of ammonia bodies in 

 the excreta. 



(2) In birds, such as the goose, there is a connecting vein between 

 the portal vein and the inferior vena cava. Ligature of the portal 

 vein on the liver side of this connection diverts the contents of the 

 portal system into the inferior cava. Under these circumstances, 

 there occurs in birds a marked diminution in the excreta of the amount 

 of uric acid, the homologue of urea in the mammal, and a corresponding 

 increase in the amount of ammonium compounds. 



(3) In mammals, a similar condition of affairs may be brought 

 about by the operation devised by Eck, and known as Eck's fistula. 

 The operation consists in making a communication between the portal 

 vein and the inferior vena cava. As before, the portal vein is ligated 

 as it enters the liver, and the portal circulation is thereby deviated 

 from the liver. Under these circumstances, the amount of urea is 

 greatly decreased in the urine, the ammonia content being greatly 

 increased. It is generally stated that animals upon which this experi- 

 ment has been performed show marked symptoms of metabolic dis- 

 turbance, accompanied by signs of ferocity and bad temper. This 

 apparently depends upon the nature of the diet given after the opera- 

 tion. Dogs which have had such an experiment performed upon 

 them, with the hepatic artery and vein ligated in addition, remain 

 for many days after the operation quite happy and docile so long as 

 they were fed on bread and milk. During this time they were becom- 

 ing progressively thinner. Any form of meat in the diet, however, 



