THE URINARY TRACT 277 
outward toward the renal capsule. Thus it is immaterial 
whether there be or be not an obstruction lower down. 
Such forms of nephritis are infiltrative, frequently puru- 
lent and are dependent upon pyelitis or the settling of 
bacteria in the deepest parts of the medulla. 
Three explanations are given in human medicine for 
the origin of this lesion. Some observers assume a direct 
transmission of bacteria up the ureter from an infected 
bladder or urethra, in a direction contrary to the urinary 
current. This, it is believed by some can occur only in the 
presence of physical obstruction, stone, kink, or pressure 
of adjacent masses upon the ureter, whereby its blood 
supply is damaged and infection facilitated. Others 
would explain the path of infection as the lymphatics of 
the ureteral wall which are infected at the opening in the 
bladder by a deep seated cystitis or by infection from a 
periproctitis or from the female genitalia. Still another 
explanation is offered by those who do not credit ascend- 
ing infections. They would have it that pyelitis arises 
from bacteria in the blood stream and only in the presence 
of injury (calculus), ureteral dilation (slowly progressive 
stenosis, or kinks, floating kidney, pressure by pregnant 
uterus) and similarly operative factors. There should 
be excluded from this category cases of chronic nephroli- 
thiasis, and of stone only in the pelvis. Under such con- 
ditions it is inevitable that a low grade of fibrosis with 
damage to the secretory structures should exist, even in 
the absence of active bacterial invasion. The cases are 
only important for our present subject when active 
bacterial infection is implanted upon them. 
Among our autopsies there have been found fourteen 
cases of ascending nephritis and seven cases of pyelitis ; 
the most instructive examples are mentioned briefly as 
follows : Five of this twenty-one were associated with 
general infectious diseases (three septicemias) and pre- 
sented no evidence of ascending obstruction. Two of this 
five were a bear and a fox, the former suffering with. 
