206 EXCRETION BY THE KIDNEYS AND SKIN 



Sodium chloride is eliminated thus to the extent of about 151 

 grains daily. The sulphates are unimportant. About 25 grains 

 are excreted daily. The phosphates are more important, the 

 acid sodium phosphate being mainly responsible for the acid re- 

 action of the urine. Nitrogen and carbon dioxide are the chief 

 gases to be found. The color of urine is due to a substance, 

 urochrome, which is probably formed from hemoglobin. Some 

 mucus from the bladder is also in the urine. 



Variation in Amount and Composition of Urine. "Its 

 constitution is varying with every different condition of nutrition, 

 with exercise, bodily and mental, with sleep, age, sex, diet, res- 

 piratory activity, the quantity of cutaneous exhalation, and in- 

 deed with every condition which affects any part of the system. 

 There is no fluid in the body that presents such a variety of con- 

 stituents as a constant condition, but in which the proportion of 

 these constituents is so variable" (Flint). 



Prolonged bodily exercise will increase the amount of urea, 

 but the urine is generally decreased in quantity because perspi- 

 ration is more active. The young child discharges relatively 

 much more urea and urine than the adult. The female dis- 

 charges relatively more urine, but less urea, than the male. Di- 

 gestion increases the urinary flow. Climate and season act chiefly 

 though increasing or diminishing cutaneous activity. Emotions 

 of various kinds may give rise to an abundant flow of pale urine. 



Discharge of Urine. On leaving the pelvis of the kidney the 

 urine enters the ureters and passes through them to the bladder, 

 whence it is discharged per urethram. 



The ureters run, one from each kidney, downward and slightly 

 inward behind the peritoneum, a distance of some 18 inches to 

 the base of the bladder. In the female the cervix uteri lies be- 

 tween the two ureters just before they enter the bladder. They 

 penetrate the bladder wall obliquely, their course therein being 

 nearly an inch long. The effect of this arrangement is that dis- 

 tention of the bladder closes the opening more closely instead 



