MECHANISM OF THE PRODUCTION OF URINE. 403 



dent that they bear directly upon the mechanism of excretion. It is not assumed, how- 

 ever, that excrementitious principles are not formed by the disassimilation of the tissues, 

 but it is asserted that urea and the nrates are produced in the kidneys by a transforma- 

 tion of excrementitious matters which exist in the blood. 



The original experiments of Prevost and Dumas are very strong arguments in favor 

 of the view that has been so long almost unquestioned, viz., that urea is simply separated 

 from the blood by the kidneys ; but the more recent observations of Bernard and Barres- 

 wil, Robin, and many others, while they confirm the first experiments on this subject, 

 have added very considerably to our knowledge of the mechanism of uraemic poisoning 

 after extirpation of the kidneys. The kidneys, it has been found, can readily be removed 

 from living animals (dogs, cats, rabbits, etc.) without any great disturbance immediately 

 following the operation. Bernard and Barreswil found that animals from which both 

 kidneys had been removed did not usually present any distinctive symptoms for a day or 

 two after, except that they vomited and passed an unusual quantity of liquid from the 

 intestinal canal. During this period, the blood never contained an abnormal quantity 

 of urea ; but the contents of the stomach and intestine were found to be highly ammo- 

 niacal. During this time, also, the secretions from the stomach and intestines, particu- 

 larly the stomach, became continuous, as well as increased in quantity. Animals oper- 

 ated upon in this way usually live for four or five days, and they then die in coma follow- 

 ing upon convulsions. Toward the end of life, the secretion of gastric and intestinal fluids 

 becomes arrested, probably from the irritating effects of ammoniacal decomposition of 

 their contents, and then, and then only, urea is found to accumulate enormously in the 

 blood. 



It is thought by Bernard that the hypersecretion by the gastric and intestinal mucous 

 membrane, in nephrotomized animals, is an effort on the part of the system to eliminate 

 urea, which is decomposed by contact with these membranes into carbonate of am- 

 monia. This view is sustained by the fact that, when urea is introduced into the alimen- 

 tary canal in living animals, it disappears almost immediately and is replaced by the am- 

 moniacal salts. Consequently, after removal of the kidneys, we should not expect to find 

 an increased quantity of urea in the blood until its elimination by the mucous membrane 

 of the alimentary canal has ceased ; but the fact that it then accumulates in large 

 quantity cannot be doubted. 



The results obtained by other experimenters generally correspond with those of Ber- 

 nard and Barreswil. It has also been ascertained, as was shown by Segalas and Vau- 

 quelin, that urea is an active diuretic when injected in small quantity into the veins of a 

 healthy animal ; and that, in this case, it does not produce any poisonous effects, but is 

 immediately eliminated. But, when urea is injected into the vascular system of a ne- 

 phrotomized animal, it produces death in a very short time, with the characteristic symp- 

 toms of ura3mic poisoning. We have frequently removed both kidneys from dogs, and, 

 when the operation is carefully performed, the animals live for from three to five days. 

 In some instances, they have been known to live for twelve days or even longer ; but 

 death always takes place finally with symptoms of blood-poisoning. 



The experiments which are supposed to show that urea and the urates are actually 

 formed in the kidneys, to which we have already alluded, were made with the view of 

 comparing the effects of removal of both kidneys with those produced by tying the 

 ureters. According to these observations, the blood contains much more urea after the 

 ureters are tied than after removal of the kidneys. These experiments, which are di- 

 rectly opposed in their results to the well-considered observations of Prevost and Du- 

 mas, Bernard and Barreswil, Segalas, and many others, cannot be accepted, unless it 

 be certain that all the necessary physiological conditions have been fulfilled. In the 

 first place, it was positively demonstrated, as early as 1847, that urea does not accumu- 

 late in the blood immediately after removal of the kidneys, but that this occurs only 

 toward the end of life, and then urea is found in enormous quantity. In the second 



