THE URINARY TRACT 273 
and vascular deficiencies to lie at the root of chronic 
interstitial nephritis. 
The origin of acute nephritis of chiefly degenerative 
character seems best explained by reference to some form 
of toxemia, whereas exudative processes, be they in 
glomerulus or supporting structures, seem to depend 
upon the direct action of bacteria. The origin of a chronic 
nephritis cannot be explained quite so readily. No one 
has answered with complete satisfaction whether a 
chronic process always begins with and proceeds from a 
single attack of acute disease, whether many acute 
attacks succeed upon one another or whether many small 
crops of agents successively attack the organ over a long 
time. Nor has an adequate explanation of the role of 
damaged blood vessels been given. It is reasonably easy 
in man to discover the existence of nephritis and of a 
possible cause; this is only true of acute cases in wild 
animals. Focal infections, those which might be the point 
of mobilization for bacteria sent to the kidneys, are fre- 
quently found in man but with exception of an occasional 
carious tooth, or a chronic osteitis are to be localized with 
difficulty in lower animals. In so far as the role of a single 
acute attack in the causation of chronic disease is con- 
cerned our material offers nothing, but some collateral or 
presumptive evidence may be mustered in regard to 
multiple infections. 
Wild animals do not give evidence of repeated attacks 
of acute disease and indeed it would seem that they more 
often die of an acute infection than live to have it 
repeated. Evidences of chronic infection, not focal, are 
reasonably definite in forty-eight per cent, of the cases 
of chronic nephritis encountered here. This suggests 
strongly that in this material protracted infectious states 
offer opportunities for renal damage of progressive char- 
acter. Vascular disease has been found twenty-eight 
times (see also section on arteries), in twenty-six of which 
the nephritis seemed due to or advanced by the damage to 
