272 DISEASE IN WILD MAMMALS AND BIRDS 
ceptible to etiological agents so that when one side is 
affected its fellow seems always to participate or to 
follow. It seems desirable in studying nephritis to eval- 
uate fully the mutual relations of functionating and sup- 
porting tissues and of the various sections of the first 
named. It is taught in many places that inflammations 
of one or another of these parts may occur independently, 
as for example a tubular nephritis, a glomerulonephritis 
and an interstitial nephritis. If however one reflect upon 
the dependence of the tubular fmiction upon the glomer- 
ulus and vice versa or upon the effect of inflammatory 
exudates in the supporting tissues upon the blood supply 
of the tubule, it becomes evident that only the most 
trivial or evanescent pathological changes in one can be 
without effect upon the others. It is difficult to see how, 
for examples, a glomerulus could remain normal if its 
associated tubule were destroyed or how if round cell 
infiltration or pus surround a capsule for any length of 
time, this structure could fail to be doomed. All this is 
by way of directing attention to the progress of physi- 
cal damage in a kidney which has received injury sufficient 
to cause nephritis, but of course it does not explain 
the cause. 
In classification of nephritis different commentators 
have employed different standards according as they 
viewed the acuteness or chronicity of the process, or as 
the principal functionating structures, glomerulus, tubu- 
lar epithelium, blood vessels, or supporting connective 
tissues, presented the most conspicuous changes. To 
these, clinicians have added phenomena of constitutional 
complication or of direct renal insufficiency. These latter 
being unavailable for us, we must fall back upon a 
classification based upon physical changes and to this end 
we have always used a slight modification of the Weigert 
method. This classification offers little in the direction 
of etiology except that toxins are believed to cause 
tubular changes, bacteria to produce glomerular lesions 
