THE KIDNEYS SECRETION OF URINE. 513 



that it may take place to some slight extent from a conversion of krcatin ; 

 though when this was given with food it was eliminated partly unchanged 

 and partly converted into kreatiniu. He found an increase in the quantity 

 of lire a in the blood, and also discovered it in the muscles, both after extir- 

 pation of the kidneys and after ligature of the ureters: the amount being 

 larger in proportion to the lateness of the period at which death occurred, 

 and on that account it was smaller in amount after ablation of the kidneys. 

 In one instance, after extirpation had been performed, he collected the whole 

 of the retained urea, and obtained 5.3 grammes, whilst if the animal had 

 been allowed to live, he would have eliminated 5.8 grammes in the same 

 space of ti-iie. Tlicr? v;:v:- certainly no increase of.kreatin after either extir- 

 pation or ligature. The respiration of oxygen diminishes the quantity of 

 urea in the urine, 1 notwithstanding that it augments the activity of the coin- 

 bustive processes, and might therefore be expected to increase it. A possi- 

 ble explanation is that it probably leads to the combustion of the urea itself 

 and its conversion into carbonic acid, ammonia, and water. The non- 

 increase of urea in the urine when violent exertion is made is, perhaps, ex- 

 plicable on the same view. On the whole, the results of recent researches 

 seem to show that urea is formed in the tissues generally, including the renal, 

 and with the exception perhaps of the muscular, and that thus entering the 

 blood from many quarters, it is filtered off by the kidneys, the secreting cells 

 of which have a special affinity for it. 



414. 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 

 being continually 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 contain, 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 organiza- 

 tion. But the kidney also serves as the channel for the elimination of saline 

 com pounds introduced into the system perse; 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 Sulphates 

 usually constitute, as we have seen ( 410), at least 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 to 

 be detected by chemical tests. The causes which influence their amount 

 have been cai'efully studied by Dr. Bence Jones; who has shown that they 

 vary (like urea) with the amount of food ingested, and with the degree of 

 nervo-muscular activity put forth ; as might be anticipated from the fact, that, 

 under ordinary circumstances, the sulphuric acid is entirely formed within the 

 system, by the oxidation of the sulphur of the protein-compounds, the bases 

 being furnished by the alkaline carbonates or phosphates of the blood. A 

 portion of the sulphur is, however, eliminated by the bowels in the form of 

 tauriu. In Mr. Weston's case the average excretion of sulphuric acid for five 

 days before his long walk of 317i miles in five days was 38.37 grains, for the 

 five days of the walk 53.50 grains, and for the five days after the walk 49.02 



1 Putter, Kevue Scientif., 1872, p. 91. 



