THE URINARY ORGATfS. 631 



Although there is no sharp line of separation, either clinical or mor- 

 phological, to be drawn between acute and chronic diffuse nephritis, it 

 is convenient to group kidney lesions in this way with the understanding 

 that many intermediate forms exist, as must be the case, since, as we 

 have seen, acute nephritis may pass gradually into the chronic form. 



While acute diffuse nephritis may be followed by the alterations 

 which have just been summarized and which are characteristic of certain 

 phases of chronic diffuse nephritis, the latter process, it should be remem- 

 bered, is by no means always or usually preceded by an acute form of in- 

 flammation. 



In some phases of chronic diffuse nephritis, although interstitial 

 alterations are present, the lesions of the tubules may be the most prom- 

 inent feature ; thus albuminous and fatty degeneration, disintegration, 

 flattening and peeling of the epithelium, the formation of casts, the dila- 

 tation of the tubules, etc., may be most conspicuous. In another mor- 

 phological group of kidneys in chronic diffuse nephritis, while there are 

 many alterations in the tubules, the most marked change is the increase 

 in amount and the subsequent contraction of the interstitial fibrous tissue 

 with atrophy of the tubules and glomeruii and the consequent diminu- 

 tion in size and alteration in shape and consistence of the organ. Be- 

 tween these extremes of lesion there are all intermediate forms, in 

 kidneys which are larger than normal, of normal size, or smaller than 

 normal. 



In endeavoring to classify or group the lesions in chronic diffuse 

 nephritis, one encounters difficulties similar to those which beset a like 

 attempt in the acute forms of renal inflammation. But the difficulties are 

 enhanced in the former case by the fact that the conditions under which 

 the lesions develop are far more diverse and variable and at the same 

 time are often much more obscure. 



If we leave out of sight for the moment the conditions under which 

 chronic diffuse nephritis may arise and the direct excitants which with 

 more or less certainty can be fixed upon as important and confine our 

 attention to morphology, it is at least convenient to place in one group 

 as above indicated kidneys in which, while there may be important 

 changes in the glorneruli and in the interstitial tissue, the most marked 

 lesions are in the tubular epithelium. This may conveniently be called the 

 parenchymatous or degenerative type of chronic diffuse nephritis. 



On the other hand, there is another large and important class of kid- 

 neys which are characterized morphologically by a relatively prominent 

 increase in the amount of interstitial fibrous tissue with associated destruc- 

 tion by atrophy or otherwise of the tubular structures. This may be 

 called the interstitial type of chronic diffuse nephritis. 



In considering this in many respects artificial grouping of persistent 

 inflammatory kidney lesions, it should be remembered that while the 

 parenchymatous and the interstitial types of lesion may originate as such 

 and so persist, the lesion of the parenchymatous type may, as the disease 

 progresses, assume the characters of the interstitial form. 



