386 PHYSIOLOGICAL CHEMISTRY. 



a small amount of the salts passes through, the glomeruli Mal- 

 pighii, while the chief part of the solids is secreted by the epithe- 

 lium of the urinary passages. A secretion of solids without a simul- 

 taneous secretion of water is not possible, and therefore a part of 

 the water must be secreted by the epithelium-cells of the urinary 

 passages. The passage of the chief part of the water through the 

 glomeruli is rather generally considered as a filtration due to blood- 

 pressure. According to HEIDEJ^HAIN", the thin cell-layers of the 

 glomeruli have a secretory action. 



The amount and the composition of urine is liable to great 

 variation. Those circumstances which under physiological condi- 

 tions exercise a great influence are the following: the blood-pres- 

 sure, and the rapidity of the blood-current in the glomeruli; the 

 quantity of urinary constituents, especially water in the blood; 

 and lastly, the condition of the secretory glandular elements. 

 Above all, the amount and concentration of the urine depend on 

 the elimination of water. That this last may vary with the amount 

 of water in the blood, with changed blood-pressure, and with cir- 

 culatory conditions is evident; but under ordinary circumstances the 

 amount of water eliminated by the kidneys depends essentially 

 upon the quantity of water which is brought to them by the blood, 

 or which leaves the body by other exits. The elimination of urine 

 is increased by abundant drinking or if the amount of water re- 

 moved in other ways is lessened; but it is decreased by a dimin- 

 ished introduction of water, or by a greater loss of water in other 

 ways. Ordinarily in man just as much water is eliminated by the 

 kidneys as by the skin, lungs, and intestines together. At lower 

 temperatures and in moist air, since under these conditions the 

 elimination of water by the skin is diminished, the elimination of 

 urine may be considerably increased. Diminished introduction of 

 water or diminished secretion of water as in violent diarrhoea, vio- 

 lent vomiting, or abundant perspiration greatly diminishes the 

 elimination of urine. For example, the urine may sink as low as 

 500-400 c. c. per day in intense summer-heat, while after copious 

 draughts of water the elimination of 3000 c. c. of urine has been 

 observed during the same time. The average quantity of urine 

 secreted in the course of 24 hours for healthy grown men is 1500 

 c. c., and for women 1200 c. c. The minimum secretion occurs 



