THE KIDNEYS. SECRETION OF URINE. 605 



The following inferences are drawn by Prof. Lehmann from these experiments : 

 1. Animal articles of diet augment the Solid matters of the Urine. Vege- 

 table substances, and still more such as are deprived of azote, on the contrary, 

 diminish it. 2. Although Urea is a product of decomposition of the organism, 

 yet its proportions in the urine depend also on the food, for we find that a 

 richly-azotized diet considerably augments its quantity. In the above experi- 

 ments, the proportion of the Urea to the other solid matters was as 100 to 116 

 on a mixed diet; as 100 to 63 on an animal diet ; as 100 to 156 on a 

 vegetable diet; and as 100 to 170 on a non-azotized diet. 3. The quantity of 

 Uric acid depends less on the nature of the diet than on other circumstances ; 

 the differences observed in it being too slight to warrant us in ascribing 

 them to the former cause. 4. The Protein-compounds, and consequently the 

 azote of the food, are absorbed in the intestinal canal ; and what is not employ- 

 ed in the formation of the tissues, is thrown off by the Kidneys in the form of 

 Urea or Uric acid ; these organs being the chief, if not the sole channel through 

 which the system frees itself of its excess of azote. 5. The urine contains quan- 

 tities of Sulphates and Phosphates proportional to the azotized matters which 

 have been absorbed; and the proportion of these salts is sensibly increased under 

 the use of a large amount of those substances. 6. In the same circumstances, 

 the Extractive matters diminish, while their quantity is increased by the use of 

 vegetable diet; a fact which proves the influence of vegetable aliment over the 

 production of these matters in the urine. 7. The urine, after the use of animal 

 food, has a strong acid reaction, but contains little or no lactic acid and no hip- 

 puric acid. Under a vegetable diet there is more lactic acid, but it is united to 

 bases. The largest production of lactic acid is under a non-azotized diet ; and 

 most of it is then combined with ammonia. Therefore the lactic acid eliminated 

 with the urine is in great part the product of non-azotized substances not 

 entirely assimilated; but it results also in part from the decomposition of the 

 azotized substances entering into the composition of the body and the food. 8. 

 The Kidneys not only separate certain constituent parts of the organs which 

 have become inadequate for the maintenance of life, but they also expel the 

 superfluous nutritive matters that may have been absorbed. 1 



641. Besides its organic materials, the Urine contains a considerable amount 

 of /Saline matter; the excretion of which, in a state of solution, appears to be 

 one of the principal offices of the Kidney. Various saline compounds are 

 continually being introduced with the food ; and others are formed within 

 the system, by the oxidation of the Sulphur and Phosphorus of the tissues 

 or of the food, and by the combination of the sulphuric and phosphoric 

 acids thus formed, with alkaline and earthy bases which the food may con- 

 tain, usually in a state of combination with weaker acids which are otherwise 

 disposed of. Thus the Saline compounds found in the urine are to be regarded 

 as partly proceeding from the retrograde metamorphosis of the materials of the 

 tissues, after these have served their purpose in the economy, and partly from 

 that of such components of the food, as, being superfluous, do not undergo 

 organization. But the Kidney also serves as the channel for the elimination of 

 saline compounds introduced into the system per se; these being sometimes 

 normally present in the body, but ingested in too large an amount, as is often 

 the case with common Salt; whilst, on the other hand, they may be altogether 

 foreign to the composition alike of its solids and its fluids. The Alkaline Sul- 

 2)hates usually constitute, as we have seen ( 638), about 10 per cent, of the 

 whole solid matter of the Urine. Being always in solution, however, they 

 never make their presence known by the formation of sediments, and are only 



1 "Journ. fur praktische Chemie," 1842-3; see also ''Simon's Animal Chemistry," 

 translated by Dr. Day, pp. 414-420, Am. Ed. ; and Prof. Lehmann's "Lehrbuch der Phy-* 

 siologischen Chemie," band ii. p. 447. 



