518 OP SECRETION AND EXCRETION. 



gradient; and these, although normally present in but small amount, may 

 undergo a marked increase in disease, especially when the liver is insuffi- 

 ciently performing its functions, or the respiratory process is obstructed. 

 Further, we have been led to regard the Kidneys as the emunctory, not only 

 for the superfluous water of the blood, but also for those saline compounds, 

 which, having been introduced into the system or generated within it, in 

 larger amount than is compatible with the normal constitution of the blood, 

 or than is required for the reparation of the solids of the body, or for the 

 production of its fluid secretions, are only fitted for elimination. On this 

 point a very elaborate series of researches was made by Wohler, 1 who showed 

 that of the soluble salts taken into the circulation, those are most readily 

 excreted which produce a determination of blood towards the kidneys, 

 whereby an increased quantity of liquid is filtered oft' through the outlet 

 which they afford. This statement is to be extended from saline compounds, 

 to such other soluble matters as are not eliminated by preference through 

 other channels, or are present in too large an amount to find their way out 

 thence with sufficient rapidity, as Sugar and Lactic acid. In like manner, 

 too, the system makes an effort to free itself (so to speak) from various sub- 

 stances altogether foreign to it, which have been introduced into the circu- 

 lating current by absorption, and which would be injurious if retained; the 

 rate at which it does so, being in a great degree dependent upon the func- 

 tional activity of the Kidneys ( 220, 221). 



417. It is a most important fact, in a Dietetic and Therapeutic point of 

 view, that the metamorphic process, of which the greater part of the constit- 

 uents of the urine are the products, should be capable of retardation or of 

 acceleration by the presence of other substances in the blood. The former 

 appears to be the operation ofthein, which is the active principle of Tea and 

 Coffee. From various experiments, 2 it appears that the use of these sub- 

 stances, by retarding the "waste" of the system, diminishes the demand for 

 food, and makes a limited amount of it go further ; 3 and this conclusion seems 

 fully borne out by experience.* The like results happen, according to Dr. 

 Bocker, under the use of small quantities of Alcohol frequently repeated ; as 

 much as 13y grammes less urea being excreted daily, when a teaspoonful of 

 proof spirit was taken seven or eight times a day, than when water alone 

 was drank. It does not hence follow, however, that Alcohol can be used as 

 advantageously for this purpose as Tea or Coffee; in fact, it may be doubted 

 whether it is so much by diminishing the "waste" of matter, as by inter- 

 fering with the due elimination of its products, that Alcohol occasions a 

 diminution in the weight of the urinary solids. For, although it does not 

 appear to effect any marked diminution, but rather an increase in the elim- 

 ination of certain forms of excrementitious matter which have been received 

 back into the blood, and especially of the hydrocarbonaceous products 

 ( 311, vi), yet very cogent evidence is supplied by the experience of Zymotic 

 diseases, that the very same cause produces an accumulation of fermentable 

 azotized substances in the blood ( 71). It seems not unlikely that the 

 almost instinctive craving for Tobacco among a large proportion of nian- 



1 Mullen's Elements of Physiology, translated by Billy, p. 589. 



2 Bocker, Archiv des Vereins tiir gem. Arbeit xur Ford, der Wiss. Heilk., 1854 ; 

 and Julius Lolimimn, Annal. der Cliein. und I'harm., Bd. Ixxxviii. 



3 Dr. Ed. Smith (Proceed, of Roy. Soc., 1801) found the decrease in the elimina- 

 tion of urea after the use of tea (which had the greatest effect) and coffee, to be but 

 slightly marked after the first day or two. 



4 Voit, from experiments with coffee on a dog, was led to a different result ; and 

 considers that this substance possesses but little influence on the excretion of urea. 

 See Henle and Meissner, Bericht, 1800, p. 397. 



