332 EXCRETION 



extirpation of the spleen (Flint). After extirpation of one kidney, it 

 has been observed that the remaining kidney increases in weight, al- 

 though investigations have shown that this is due mainly to an increase 

 in the quantity of blood, lymph and urinary matters, and not to a new 

 development of renal structure. 



Influence of Blood-pressure, the Nervous System etc., on the Secretion 

 of Urine. There are many instances in which marked and sudden 

 modifications in the action of the kidneys take place under the influence 

 of fear, anxiety, hysteria etc., which must operate through the nervous 

 system. Although little is known of the final distribution of the nerves 

 in. the kidney, it has been ascertained that here, as elsewhere, vasomotor 

 nerves are distributed to the walls of the bloodvessels, and they are 

 capable of modifying the quantity and the pressure of blood in these 

 organs. 



It may be stated as a general proposition, that an increase in the 

 pressure of blood in the kidneys increases the flow of urine, and that 

 when the blood-pressure is lowered, the 'flow of urine is correspond- 

 ingly diminished. This will in a measure account for the increase in 

 the flow of urine during digestion ; but it can not serve to explain all the 

 modifications that may take place in the action of the kidneys. 



Inasmuch as the excrementitious matters eliminated by the kidneys 

 are being constantly produced in the tissues by the process of katabo- 

 lism, the formation of urine is constant, presenting, in this regard, a 

 marked contrast with the intermittent flow of most of the secretions 

 proper as distinguished from the excretions. It was noted by Erichsen, 

 in a case of extroversion of the bladder, and it has been further shown 

 by experiments on dogs, that there is an alternation in the action of the 

 kidneys on the two sides. Bernard exposed the ureters in a living ani- 

 mal and fixed a small silver tube in each, so that the secretion from 

 either kidney could be readily observed ; and he noted that a large 

 quantity of liquid was discharged from one side for fifteen to thirty 

 minutes, while the flow from the other side was slight and in some 

 instances was arrested. The flow then began with activity on the other 

 side, while the discharge from the opposite ureter was diminished or 

 arrested. 



Physiological Anatomy of the Urinary Passages. The excretory 

 ducts of the kidneys the ureters begin each by a funnel-shaped 

 portion, which is applied to the kidney at the hilum. The ureters 

 themselves are membranous tubes of about the diameter of a goose- 

 quill, becoming much reduced in calibre as they penetrate the coats of 

 the bladder. They are sixteen to eighteen inches (40 to 46 centimeters) 

 in length, and pass from the kidneys to the bladder, behind the peri- 



