644 OF SECRETION. 



much waste of the Nervous System, is followed by an increase in the quan- 

 tity of the alkaline Phosphates in the Urine ( 295). This increase cannot 

 proceed from the waste of the Muscular system ; for this would set free 

 Phosphate of Lime, which chiefly passes off by the fasces. 



848. The alkaline or acid reaction of the Urine, therefore, will not only 

 depend upon the quantity of alkaline Phosphates converted into acid Phos- 

 phates by the Uric and Hippuric acids ( 845) ; but also upon the amount of 

 the bases in the ingesta, compared with that of the permanent Acids intro- 

 duced into the system or generated within it. The Urine of animals which 

 live chiefly or entirely upon Vegetable food, is almost invariably alkaline; 

 because this food contains a large quantity of alkaline bases, in combination 

 with Citric, Tartaric, Oxalic, and other acids, which are decomposed within 

 the system ; and the amount of Sulphuric and Phosphoric acids produced is 

 not sufficient to neutralize them. On the other hand, the food of Carnivo- 

 rous animals contains no free or weakly-combined bases ; and as its Sulphur 

 and Phosphorus, when oxidized in the system, produce a considerable quan- 

 tity of free acids, which share the bases with the Muriatic acid already there, 

 the Urine must necessarily have an acid reaction. The character of the 

 Urine of Man, in this respect, is considered by Liebig to depend entirely upon 

 that of the food ingested. 



a. Proceeding upon his determination that no Lactic acid is ever present in the Urine, he 

 remarks : " The acid, neutral, or alkaline reaction of Urine of healthy individuals, does not 

 depend on any difference in the processes of digestion, respiration, or secretion, in the va- 

 rious classes of animals, but upon the constitution of the aliments, and upon the alkaline 

 bases which enter the organism through the medium of these aliments. If the amount of 

 these bases is sufficiently large to neutralize the acids formed in the organism, or supplied 

 by the aliments, the urine is neutral ; whilst it manifests an alkaline reaction, when the 

 amount of alkaline bases thus supplied to the organism is more than sufficient to neu- 

 tralize the acids; but in all these cases, the urine accords with the nature of the aliments 

 taken." The varying amount of Uric Acid, which, on Prof. Liebig's own showing, is very 

 much influenced by the respiration, is altogether left out of consideration in this sweeping 



generalization. 



849. The amount of Azotized matter in the Urine, also, is greatly influ- 

 enced by the nature of the food ingested, whilst the constitution of the Ani- 

 mal frame remains nearly the same ; hence it appears, that a certain portion 

 of it must be derived from the unassimilated materials which have been taken 

 into the blood, and which, being superfluous, are injurious. It is well known 

 that the ingestion of an over-supply of azotized matter does not occasion an 

 increased production of the fibrinous or gelatinous tissues ; and it may be 

 hence inferred that, as there is no means by which the superfluous amount 

 can be stored up in the system (in the mode that non-azotized matter is stored 

 up as Fat), it must be continually eliminated from the Blood. And there can 

 be no doubt that the Kidneys are the principal channel by which this is ef- 

 fected ; the amount of azote thrown oft' in a given time, in the various com- 

 pounds which they excrete, being equal to 10-1 Iths of the whole quantity 

 ingested. The following are the results of the most satisfactory inquiries 

 that have yet been made, in regard to the influence of various kinds of Ali- 

 ment upon the amount of the solid matters in the Urine. These experiments 

 were performed by Dr. Lehmann of Leipsig, upon himself. In thejirsl series, 

 Dr. L. adopted an ordinary mixed diet ; but he took no more solid or liquid 

 aliment than was needed to appease hunger or thirst, and abstained from fer- 

 mented drinks. Every two hours he took exercise in the open air, but he 

 avoided immoderate exertion of every kind. The average result of the exa- 

 mination of the Urine passed under these circumstances, for fifteen days, is 

 given in the first line of the subsequent Table. In a second series of experi- 

 ments, Dr. L. lived for twelve days on an exclusively Animal diet ; and for 



