SECRETION OF URINE. 539 



to the former cause. 4. The combinations of Proteine, and consequently the 

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

 ployed 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 quantities of Sulphates and Phosphates proportional to the azotized 

 matters which have been absorbed ; and the proportion of these salts is sensi- 

 bly increased under the use of a large amount of those. 6. In the same cir- 

 cumstances, 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. Under an animal 

 diet, the quantity of Lactic acid diminishes ; but the greater part of this acid 

 is free. It is the reverse 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."* 

 It seems right to remark, with regard to these inferences, that all the statements 

 concerning the amount of Lactic acid and the Lactates must be received with 

 hesitation, in consequence of the statements of Liebig already referred to. 

 The most unequivocal facts determined by Dr. Lehmann's inquiries, are those 

 which relate to the influence of Diet on the amount of Urea excreted. The 

 experiments upon a purely non-azotized diet were not continued long enough 

 for a satisfactory result to be obtained ; but it is evident that, so long as the in- 

 gesta contain no azote, the whole of that element in the Urine must be attributed 

 to the disintegration or waste of the Tissues, and may be fairly taken as a 

 measure of its amount. 



681. The fact of the pre-existence of the chief constituents of Urine in the 

 Blood, is important as explaining the facility with which the secreting function 

 appears to be transferred to other membranes, in some of the cases in which 

 the Kidney does not perform its function. Doubtless there has been much 

 error on this subject, arising out of deceptions practised by impostors; but a 

 sufficient number of indubitably genuine cases are on record, to put it beyond 

 doubt that such transferences have taken place, urinous fluid being secreted 

 from the stomach, mammae, umbilicus, nose, &c.t On the other hand, the 

 Kidney may serve as the channel for the elimination of substances, which are 

 usually drawn off by other organs. Thus, when the secreting action of the 

 Liver has been gradually impaired by structural disease, the Kidneys appear 

 to have performed their function, in separating some (at least) of the elements 

 of Bile. And a case has recently been mentioned, in which the urine of a par- 

 turient female, who did not suckle her infant, was found to contain a conside- 

 rable amount of Butyric acid, during several days. The elimination of Kies- 

 tene by the Kidney during pregnancy will be presently noticed ( 690J. 



682. The facility with which substances taken into the current of the Cir- 

 culation pass into the Urinary secretion, varies extremely ; and no general law 

 can be stated in regard to it. It appears from Woehler's elaborate researches 

 on this subject, that the salts which are most readily excreted are those which 

 excite the action of the kidneys.:}: The rapidity with which absorption and 



* L'Experiqrice, Dec. 7, 1843; andEdinb. Monthly Journal, March, 1844. 



j- For a scientific explanation of this fact, see Princ. of Gen. and Comp. Phys., 539. 



* See Muiler's Physiology, p. 589. 



