276 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



Drechsel supposes, however, that this dehydration is effected in an indirect 

 manner; that there is first an oxidation removing two atoms of hydrogen, 

 and then a reduction removing an atom of oxygen. He succeeded in showing 

 that when an aqueous solution of ammonium carbamate is submitted to elec- 

 trolysis, and the direction of the current is changed repeatedly so as to get 

 alternately reduction and oxidation processes at each pole, some urea will be 

 produced. These facts show the existence of ammonium carbamate in the 

 body, and the possibility of its conversion to urea. Recent experiments made 

 by Hahn, Pawlow, Massen, and Nencki 1 show that in dogs removal of the 

 liver is followed by the appearance of carbamates in the urine and a marked 

 decrease in the amount of urea. In these remarkable experiments a fistula was 

 made between the portal vein and the inferior vena cava, the result of which 

 was that the whole portal circulation of the liver was abolished, and the only 

 blood that the organ received was through the hepatic artery. If, now, this 

 artery was ligated or the liver was cut away, as was done in some of the ex- 

 periments, then the result was practically an extirpation of the entire organ an 

 operation which has always been thought to be impossible with mammals. The 

 animals in these investigations survived this operation for some time, but they 

 died finally, showing a series of symptoms which indicated a deep disturbance 

 of the nervous system. It was found that the symptoms of poisoning in these 

 animals could be brought on before they developed spontaneously by feeding 

 the dogs upon a rich meat diet, or with salts of ammonia or carbamic acid. Later 

 investigations 2 showed that in normal animals the ammonia contents of the 

 blood in the portal vein are from three to four times what is found in the arte- 

 rial blood, but that after the operation described the ammonia in the arterial 

 blood increases and at the time of the development of the fatal symptoms 

 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 (ammonium carbamate) accumulates in the blood and 

 causes 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 ammonium carbamate there is little direct evidence. It comes in the long 

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

 DrechsePs supposition is 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 



1 Archivfur experimentdle Pathologie und Pharmakologie, 1893, Bd. xxxii. S. 161. 



2 Nencki, Pawlow, and Zaleski: Ibid., 1895, Bd. xxxvii. S. 26. 



