1893.] 



Urea in the Blood of Birds, 8fc. 



481 



If this is again dissolved in distilled water and the solution intro- 

 duced into a small ureometer filled with the solution of hypobromite 

 of sodium, the quantity of nitrogen given off can be readily deter- 

 mined and the amount of urea in the solution can be deduced from 

 it. 1 gramme of urea equals 0*46 gramme of nitrogen, or 372*7 c.c. 

 In practice, however, 354*3 c.c. have been obtained. 



If, on the other hand, we wish to crystallise the salt and directly 

 weigh the amount, this is best effected by adding a few drops of nitric 

 acid to the urea solution, so causing the formation of nitrate of urea. 

 This can be weighed, after purification, by redissolving it in absolute 

 alcohol. 



The fact that the residue left after evaporation is undoubtedly 

 nitrate of urea is proved by the characteristic form of the crystals 

 (either simple rhomboids or aggregated varieties of these), or by a 

 microscopic test which I have adopted of adding a drop of the hypo- 

 bromite of sodium to the crystal under the microscope, and seeing the 

 innumerable bubbles of nitrogen which are given off. 



The following table shows the amount of urea found in a hundred 

 parts of the blood of different mammals and birds : — 



Sheep. . . . 



0*029 per cent. 



Fowl 



0*025 per 



cent. 



Sheep. . . . 



0*025 



Turkey . . . 



0*026 



55 



Ox 



0*022 



Duck 



0*029 



55 



Ox 



0*021 



Turkey . . . 



0*024 



55 







Fowl . , , 



0*026 



55 







Duck 



0*020 



55 







Fowl , , 



0*026 



55 







Goose 



0*020 



59 







Turkey . . . 



0*022 



55 



It will be seen that, if we compare these results, the amount of 

 urea in the blood of the mammal and of the bird is practically 

 identical. 



It has been found that in normal human blood the urea varies from 

 0*020 to 0*040 per cent. My results, obtained from the different 

 animals above mentioned, are all within these limits. 



When urea is introduced into the stomach of a mammal, it is 

 eliminated by the kidneys in an unchanged form. This has repeat- 

 edly been shown to be the case, and the fact is not questioned by 

 physiologists. On the other hand, when urea is introduced into the 

 stomach of a bird, or other uric- acid- excreting animal, it is not thrown 

 out in the form in which it is introduced ; but there is, instead, an 

 increased formation of uric acid. This has been shown to be the case 

 by H. Meyer and M. Jaffe * 



Next with regard to uric acid. 



* In the 'Berichte d. Deutschen Chem. G-esellschaft,' vol. 10, 1877, p. 1930. 



