CHEMISTRY OF DIGESTION AND NUTRITION. 337 



reaches about the percentage which is normal to the blood of the portal vein. 

 It would seem from these investigations that the liver stands between the 

 portal circulation and the general systemic circulation and protects the latter 

 from the comparatively large amount of ammonia compounds contained in the 

 portal blood by converting these compounds to urea. If the liver is thrown 

 out of function, ammonia compounds accumulate in the blood and cause 

 death. The rich amount of ammonia in the portal blood seems to come 

 chiefly from the decomposition of proteid material in the glands of the 

 stomach and pancreas during secretion. Similar ammonia salts are probably 

 formed in other active proteid tissues, since the percentage of ammonia in the 

 tissues is considerably greater than in the blood, and these compounds also are 

 doubtless converted to urea in the liver, in part at least. As to the origin of 

 the ammonia compounds there is little direct evidence. They come in the long 

 run, of course, from the nitrogenous food-stuffs, proteids and albuminoids. 

 Drechsel, having reference to one form only, namely, ammonium carbamate, 

 supposes that the proteids first undergo hydrolytic cleavage, with the formation 

 of amido- bodies, such as leucin, tyrosin, aspartic acid, glycocoll, etc.; that 

 these bodies undergo oxidation in the tissues, with the formation of 

 NH 3 , C0 2 , and H 2 ; and that the XH :j and CG 2 then unite synthetically to 

 form ammonium carbamate, which is carried to the liver and changed to 

 urea. There is reason to believe that the formation of ammonia compounds 

 takes place in the tissues generally. 



2. Even after the removal of the liver some urea is still found in the urine. 

 This fact proves that other organs are capable of producing urea, but what the 

 other organs are and by what process they make urea are points yet undeter- 

 mined. It seems probable that some of the ammonia compounds which are 

 now known to be formed in the tissues generally and to be given off to the 

 blood may be converted into urea elsewhere than in the liver. Just as the 

 glycogenic function of the liver-cells is shared to a less extent by other tis- 

 sues — e. g. the muscle-fibres — it is possible that their power of converting 

 ammonia salts to urea may be possessed to a lesser degree by other cell-, and 

 for this reason removal of the liver is not followed at once by a fatal result. 

 Concerning this point, however, we must wait for further investigation. 

 Drechsel has recently called attention to a method of obtaining urea directly 

 from proteid outside of the body. Mis method is interesting not only 

 because it is the first laboratory method discovered of producing urea from 

 proteid, but also because it is possible that substantially the same process may 

 occur inside the body. The method consists, in brief, in fust boiling the pro- 

 teid with an acid; IIC1 was used, together with some metallic zinc, so ;i- to 

 keep up a constant evolution of hydrogen and to exclude atmospheric oxygen. 

 Among the products of decomposition of the proteid thus produced was a 

 substance termed lysatinin (C 6 H u N s O), and when this body was isolated and 

 treated with boiling baryta-water (Ba(OH) 2 ) some urea was obtained. It is to 

 be noted that in this case the urea was obtained not by the oxidation of the 

 proteid, but by a series of decompositions or cleavages of the proteid molecule. 

 Vol. I.— 22 



