512 OF SECRETION AND EXCRETION. 



and are not merely adapted for the elimination of water, since these glo- 

 meruli are abundantly distributed through the kidneys of birds, the urine of 

 which animals is semisolid, whilst it is impossible to obtain a trace of uric 

 acid from their blood. Now, in opposition to some of these statements are 

 the observations of G. Meissner, 1 who, by analyzing large quantities of blood, 

 obtained unmistakable evidence of the presence of uric acid in that of the 

 bird (goose), and shows by calculation that it is possible for all the uric acid 

 excreted by the animal' to have been separated from the blood passing through 

 the kidney in a given time. In the course of his experiments, Meissner found 

 so much uric acid in the liver, and so little in other organs, that he came to 

 the conclusion that the liver was the seat of its formation in birds. 2 On ex- 

 tending his researches to mammals, he found that here also the liver presented 

 on chemical analysis a larger proportion of the essential urinary constituent 

 urea than any other organ. Hence he concludes that it proceeds from the 

 disintegration of the haemoglobin of effete blood-corpuscles into urea, glyco- 

 geu, and biliary coloring matter ; and adduces pathological evidence, de- 

 rived from the observations of Frerichs, Stiideler, and Harley, to the effect 

 that in acute and chronic atrophy of the liver it is either greatly diminished 

 or wholly absent. Heynsius further adduced in support of this view the 

 fact that more urea can be obtained from a liver which has been removed 

 from the body for some hours and kept at a temperature of 104 F. than 

 from a fresh one, and Cyon 3 maintained that the blood which was passed 

 through the liver of a living animal is richer in urea after its passage than 

 before. These statements have, however, been again called in question by 

 Gscheidleu in an elaborate essay 4 upon the subject, and his experiments have 

 led him to the conclusion that no single organ can be fixed upon as exclu- 

 sively producing urea, but that it is formed in the system generally. It is 

 remarkable that though it can be detected in the blood, liver, spleen, kid- 

 neys, brain, and eye, it does not appear to be present in the muscles. Grehaut 5 

 finds that after extirpation of the kidneys, the amount of urea in the blood 

 undergoes progressive increase, proportionate in fact to the quantity that 

 would have been excreted had the kidneys been in action ; he finds also that 

 after ligature of both -ureters the same accumulation of urea takes place, 

 and that the renal venous blood, contrary to Picard's statement, contains 

 less urea than renal arterial blood, whilst after ligature of both ureters the 

 proportion of urea in the arterial and renal venous blood is equal. There 

 seems therefore to be good reason for believing that the urea is simply ex- 

 creted by and not formed in the kidneys. 6 In reference to the origin of 

 urea from kreatin, Meissner states, in opposition to Munk, 7 that he has found 

 no increase in the amount of urea when kreatin or kreatinin were given with 

 the food, or otherwise introduced into the blood. In all instances these sub- 

 stances were discharged either unaltered, or merely with conversion of some 

 of the kreatin into kreatinin. Voit 8 also declares himself opposed to the 

 view that the formation of urea occurs at the kidneys, except in so far as 



1 Centralblatt, 1868, pp. 226 and 275. 



8 Pawlinoft' (Centralblatt, 1873, p. 241) has satisfied himself that uric acid is not 

 formed in but only excreted by the kidneys. 



3 Centralblatt, 1870, p. 580. For a good resume of all this discussion, see Parkes's 

 Lectures, in the Lancet, 1871, vol. i, p. -467. 



4 Si-i- abstract of his memoir in Centralblatt, 1871, p. 630. 



6 Centralblatt, 1870, p. 249. 



6 See the corroborative experiments of Rosenstein, Centralblatt, 1871, p. 353; 

 Falck, Virdiow's Archiv, Bd. liii, 1871, p. 282; Gscheidlen, Studien iiber den 

 Ursprung cles Harnstoffa im Thierkorper, Leipzig, 1871. 



7 iVut-ehe KliiiiU, 1802, p. 299. 



8 Centralblatt, 1808, p. 408. 



