The mean composition of urine is stated by Becquerel as follows:— The urine of the same individual was also examined under three varying conditions, as follow: — A, on rising in the morning, several glasses of water having been drunk the pre vious evening ; B, water and some coffee taken, and violent exercise had recourse to during two hours, pulse 100, with occasional intermissions ; C, urine voided half an hour after urine B. These urines were all acid; C most so, and B the least. All three speci mens were clear, and B the least coloured.
The following is the result of the analyses : The specific gravities of the above speci mens were respectively 1010, 1008, and 1014.
Lehmann has analysed the urine collected during 24 hours, from a well-fed and healthy young man. The following three results were thus obtained by him:— Simon very properly remarks on the above analyses, that the discrepancies to be ob served in the composition of the urine, princi pally depend on the variation in the propor tion of water ; and that if we consider the pro portion of each solid constituent to the whole amount of solid matters, the differences will not appear nearly so great.
The variations caused in the urine by the ingestion of various mineral substances, and of organic compounds taken either as food or medicine, have attracted the attention of several chemists of eminence. Liebig has theorised freely on this subject, and it is but right that what he has published should be copied into this article, if only as part of the history of the urine, while I would warn the reader carefully to separate in his mind the matters of fact from the theoretical part of the subject, inasmuch as a great deal yet remains to be done. The position of the inquiry is indeed at present such, that further advances may very probably lead us to detect the fallacy of theories which, it is to be feared, the pre sent state of our knowledge may permit us to see in too attractive a form.
Liebig remarks, "When the hydrochloric acid (in the stomach) has exercised its solvent action upon the aliments, and the latter have passed into a state of solution, the soda which originally entered the organism in com bination with the hydrochloric acid, that is, as common salt, rejoins the hydrochloric acid during the preparation of the chyme, and pre vious to its transformation into chyle, the soda and the hydrochloric acid thus reunited combine again and form common salt : chyle and lymph have no longer any acid reaction, but, on the contrary, they manifest alkaline properties."4 The alkaline reaction of the lymph, chyle, and blood of man and of the car nivorous animals cannot be owing to the pre sence of a free alkali, as is evident from the preceding observations ; for the nutriments of man and of the carnivorous, as well as the graminivorous, animals, contain no free alkali, nor any salt formed of an alkaline base and an acid which might be destroyed in the organism by the vital process, and thus cause the alkaline base to be liberated. The blood
must contain the same salts as exist in the aliments. With the exception of common salt, nothing is added during the digestion of the aliments. We have seen that this substance undergoes decomposition in the upper part of the digestive apparatus, being resolved into free soda and free hydrochloric acid ; but we have also seen that the liberated soda rejoins the hydrochloric acid during the pre paration of the chyme, and previous to the transformation of the latter into chyle ; that is, when the acid has performed its function, viz. the solution of the aliments, —the salt formed by this combination, that is, common salt, has neither an acid nor an alkaline re action. The salts with alkaline reaction con tained in meat, flour, or grain, are alkaline phosphates. It is obvious that the alkaline reaction of the chyle, lymph, and blood of animals feeding upon animal and vegetable substances can only be derived from their alkaline phosphates. The serum of the blood can only be considered as a combination of albumen with an alkaline phosphate ; the fibrin of the blood, or the fibrin of the muscular fibre, is a combination of albumen with phos phate of lime.
" The bibasic phosphates of soda and of potash are in many respects highly remarkable salts. Although of a tolerably strong alkaline reaction, yet they exercise no destructive action upon the skin, nor upon organic forma tions. They possess all the properties of the free alkalies, without being such : thus, for instance, they absorb a large amount of car bonic acid, and this in such a manner that acids produce effervescence in a saturated so lution of this kind, just as they would in alkaline carbonates. They dissolve coagulated curd of milk or cheese, as well as coagulated albumen, into clear fluids with the greatest facility, just as caustic or carbonated alkalies do. But of still greater importance in relation to the secretion of urine is their deportment towards hippuric acid and uric acid. Hippuric acid dissolves with the greatest facility in water to which common phosphate of soda has been added. Uric acid possesses the same property at a high temperature; the phosphate of soda, in this process, loses its alkaline re action completely upon the addition of uric acid and hippuric acid, and assumes an acid reaction. The acid nature of the urine of man, and of the carnivorous and graminivorous animals, is thus explained in a very simple manner.