336 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



verted to urea, and gives the following evidence for this view. In the 

 firsl place, Drechsel found carbamic acid in the blood of dogs, and 

 Drechsel and Abel have shown that it occurs normally in the urine of 

 horses as calcium carbamate ; and Abel lias shown that it may be 

 found in the urine of dogs or infants after the use of lime-water. Drechsel 

 has shown, further, that ammonium carbamate may be converted into urea. 

 If one compares the formulas of ammonium carbamate ami urea, it is seen that 

 the former may pass over into the latter by the loss of a molecule of water, a — 



CO< XI F - — H = CO< XH 2. 

 OXH, - XH 2 



Ammonium carbamate. Urea. 



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, aud 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. It remain- possible, 

 however, that other salts or compounds of ammonia may likewise be con- 

 verted normally to urea by the liver, since it has been shown experimentally 

 in artificial circulation through this organ that salts such as ammonium car- 

 bonate, or even such complex ammonia compounds as leucin and glycocoll, 

 may give rise to urea. Experiments made by Halm. Pawlow, Massen, 

 and Nencki ' show that in dogs removal of the liver is followed by a 

 decrease in the amount of urea in the urine and an increase in the 

 ammonia contents. 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 tin' 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 ;i rich meat diet, or with .-alts 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 



1 Ardiir far experimentelle Pathologie and Pharmakolor/ie, 1893, Bd. xxxii. S. 161. 



2 Nenoki, Pawlow, and Zaleski : Ibid., 1895, Bd. xxxvii. S. 26; also, Xencki and Pawlow: 

 Archives '/•.-• Sciences biologiques, t. 5, p. 213. 



