602 OF SECRETION AND EXCRETION. 



generated by the retrograde metamorphosis of Muscular tissue (probably through 

 the intermediation of creatine or of uric acid), and also by similar changes in 

 the unassimilated portions of the Blood itself. 1 The amount of Urea excreted 

 in the 24 hours has been made the subject of examination by M. Lecanu : 2 and 

 the following are his results as deduced from a series of 120 analyses : 



Minimum. Mean. Maximum. 



By Men 3 . . . . . 357.51 grs. 433.13 grs. 510.36 grs. 



By Women .... 153.25 " 295.15 " 437.06 " 



By Old Men (84 to 86 years) . 61.08 " 125.22 295.15 " 



By Children of eight years . 161.78 " 207.99 " 254.20 " 



By Children of four years . 57.28 " 69.55 " 81.83 " 



It is very interesting to perceive, in this table, how large an amount of Urea is 

 excreted by children ; and how small a quantity in proportion to their bulk, by 

 old men. This corresponds precisely with the rapidity of interstitial change at 

 different periods of life. (See CHAP. in. SECT. 3.) The quantity of Urea 

 secreted at any given period of life seems to depend mainly on two conditions ; 

 namely, the degree of muscular exertion previously put forth, and the amount 

 of azotized matter ingested as food. Thus, Prof. Lehmann ascertained that, by 

 the substitution of violent for moderate, exercise, the quantity of Urea was raised 

 from 82 \ to 45 \ parts; and Simon found that, by two hours' violent exercise, 

 the proportion of the urea in the urine passed half an hour subsequently, was 

 double that contained in the morning urine. Again, Prof. Lehmann has shown 

 that the amount of Urea excreted daily, when no azotized matter was taken in 

 as food, and when the excretion was simply a measure of the "waste" of the 

 tissues, was not above half that excreted when an ordinary mixed diet was em- 

 ployed, and only about two-sevenths of that which was passed when the diet was 

 purely animal. The recent experiments of Prof. Bischof are to the same effect ; 

 for he found that a large dog secreted, with mixed food, from 230 to 300 grains 

 of urea daily; with flesh diet, 802 grains; and when fed on intestines and gela- 

 tine, no less than 1110 grains daily. This last statement confirms the inference 

 to which the injection of a solution of Gelatin directly into the blood appears to 

 lead ( 399); namely, that urea may be formed directly from the metamorphosis 



1 A new and easy method of determining the amount of Urea in Urine has lately been 

 introduced by Prof. Liebig. It is founded on the fact that urea forms with pernitrate of 

 mercury two compounds, one with 2, the other with 4 equivs. of peroxide of mercury. The 

 latter is almost insoluble ; and therefore, by adding to urine pernitrate of mercury, from 

 a solution of known strength, the urea may be precipitated and its quantity determined 

 in a few minutes. All the phosphoric acid in the urine, however, must first have been 

 precipitated by barytes ; which will also, of course, throw down its sulphuric acid. The 

 presence of a chloride prevents the action of the pernitrate on the urea, converting it into 

 a perchloride ; hence the chloride of sodium always contained in the Urine must be allowed 

 for, before the quantity of Urea can be determined. The appearance of the precipitate 

 shows when all the chlorine present has been taken into combination with the mercury ; so 

 that the quantity of the pernitrate added to produce it gives that of the common Salt, 

 while the quantity afterwards required to throw down the whole Urea gives the amount of 

 that substance. (See Prof. Gregory's "Handbook of Organic Chemistry," p. 509; and 

 Dr. Martin Barry's communication in the " Lancet," April 17, 1852.) 



2 "Journal de Pharmacie," torn. xxv. 



3 According to Prof. Bischof, of Giessen, who has employed Prof. Liebig's method of esti- 

 mating the amount of urea in Urine (described in the preceding note), the quantity ordi- 

 narily excreted daily by a healthy man is not less than 830 grains, or nearly 12 ounces 

 avoirdupois. If this be correct, the estimates of Lecanu are far below the truth, his mean 

 for men being only 433 grains, or little more than half the estimate of Bischof. Still the 

 above table will have a certain- value ; since all the amounts stated in it were obtained by 

 the same method, and may therefore be fairly compared with each other. The speedy 

 publication of Prof. Liebig's process "in a form adapted for easy and accurate use by 

 medical men" has been promised ; and it is to be hoped that a large body of valuable facts 

 will then be collected. 



