The time is gone when the ever usable and available "catching cold" might serve as an explanation for suppurations and catarrhs of the mucous membranes. We know now that while it may produce a degree of predisposition of the tissues, the real awakening of the affections in question must proceed from precisely definable poisons. These, in the vast majority of cases, are connected with microörganisms or are produced by them.
Thus "vesical catarrh from cold," which formerly was so frequently diagnosed, has disappeared from our field of vision; in like manner, purulent inflammation of the pelvis of the kidney must be attributed to pyogenic presences—bacteria or the products of their metamorphosis—impinging upon the mucous membrane. Their presence is an absolute sine qua non, without which any disturbances such as stones, foreign bodies, stasis, etc., can not produce this definite effect.
How do these pyogenic elements enter the urinary passages? As