774 SPECIAL PHYSIOLOGY. 



Under excessive pressure in the arterial blood-columns of the kid- 

 neys, as, e. g., when the aorta is tied below the points of origin of the 

 renal arteries, albumen appears in the urine. The same event hap- 

 pens from obstruction of the renal ducts or vessels, or from the pres- 

 sure of tumors upon them. This is not a dialytic process, albumen 

 being a colloid substance, and difficult to dialyze ; but it is probably an 

 example of simple porous diffusion or filtration. In acute inflamma- 

 tory conditions, fibrinous exudations from the blood form in the tubuli, 

 and appear in the urine as minute coagula or casts. 



The urine excreted into the tubuli, urged on by the vis a tergo of a 

 constant process of excretion, escapes from their orifices into the 

 calyces. From these, it descends along the infundibula, the pelves of 

 the kidneys, and the ureters, into the bladder, partly by gravity, and 

 probably partly propelled by the rhythmic peristaltic actions of the 

 muscular coat of those canals. Accumulated in the bladder, it be- 

 comes further concentrated by absorption of water, and is mixed with 

 mucus from the ducts and from that viscus. 



The constancy and the great rapidity of the excretion of urine, 

 have been observed in cases of malformation, known as inversion of 

 the bladder, in which the lower part of the abdomen and the anterior 

 portion of the urinary bladder are defective, so that the fundus of this 

 .organ, into which the ureters open, is exposed. Under ordinary cir- 

 cumstances, the urine is seen to flow in drops, from the mouths of the 

 ureters ; but, after drinking freely, it runs in little streams. 



The urinary excretion is affected, both in quantity and quality, by 

 the nervous system. Thus, it is increased in quantity, and lowered in 

 quality, by hysteria, fear, and other mental emotions, this effect being 

 probably due to dilatation of the renal arteries. Injury of the spinal 

 cord affects the urine, chiefly causing a great development of carbo- 

 nate of ammonia and the precipitation of phosphates, owing, it appears, 

 to congestion and inflammation of the bladder, with an increased se- 

 cretion of mucus from it. Complete removal of the brain and spinal 

 cord, in animals, does not much affect this excretion. 



The walls of the bladder chiefly consist of layers of unstriped 

 muscular fibres, collected into bundles, arrranged like figures of 8, on 

 the front, back, and sides of the organ. Some of these, surrounding 

 the neck, act like a sphincter ; the others form detrusor, or expellent 

 muscles. The act of emptying the bladder requires the simultaneous 

 relaxation of the one, and the contraction of the other set. These 

 are usually reflex acts, excited directly by the accumulated fluid, or 

 by some irritation of the nervous system. The act of expulsion is 

 aided by the contraction of the abdominal walls. 



The Urine. 



The daily quantity of fluid excreted by the kidneys of an adult 

 healthy man, varies from 30 oz. to 80 oz. ; but, on an average, it has 

 been estimated at about 50 oz. This quantity varies according to the 

 amount of fluid taken in the food and as beverage, the activity of ex- 

 halation by the skin and lungs, and the amount excreted by the intes- 



