Experimental infiltration of the intravesical ureter of the normal bladder in the living, anesthetized animal with magnesium sulfate or physiological salt solution caused a reflux of urine into the ureter in 6 out of 18 guinea pigs (33 per cent); in 22 out of 27 rabbits (81 per cent), and in 14 out of 17 dogs (82 per cent).

The vesical pressure necessary to produce this experimental reflux is low and ranges between 2 and 12 mm. of Hg; hydrostatic pressure of the bladder contents often sufficed to drive urine into the kidney pelvis.

After an experimental reflux had occurred, increased vesical pressure often failed to raise the level of the regurgitant column in the ureters of rabbit and dog: these higher pressures had rendered an incompetent valve competent.

Control pressures ranging between 8 and 40 mm. of Hg without a preceding infiltration, caused no reflux in the great majority of dogs.

The amount of infiltrated fluid necessary to produce reflux varied from 0.2 cc. in the guinea pig to 0.5 to 2 cc. in dog.

Spontaneous regurgitation, that is regurgitation without a preceding infiltration, was seen in 4 guinea pigs, 4 rabbits and 2 dogs.

Antiperistalsis of the ureters, that is a wave of contraction passing from the bladder to the kidney, was never seen in our animals with experimental reflux.

Biopsy of the bladder in rabbit and dog showed edema of the ureterovesical valves after infiltration in most of our animals. Hemorrhages into the submucosa in the neighborhood of the ureteral valves were observed in some. The bladders of 3 rabbits, exhibiting spontaneous reflux without infiltration showed pouting, edematous lips of the ureterovesical orifices.

The cause of experimental regurgitation is a non-obstructive edema of the vesical valve; this edema renders the valve flap more rigid and therefore incompetent at relatively low intravesical pressures. Higher intravesical pressures may again render the incompetent valve competent.

The experimental results are applied to the human subject because the urinary bladder of dog and of man are quite similar in structure and function. Reasons are presented suggesting that the described type of reflux may cause pyelitis and pyelonephritis.

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