This lumbar method is undoubtedly to be preferred when it is known that a simple nephrotomy will be sufficient or when the more or less diseased kidney is to be treated as a cyst or abscess by drainage. It is open to the objection that if it be found desirable to change the operation into an nephrectomy, it is not quite so easy to remove a large mass in this way as by laparotomy, and the pedicle is much less accessible. The objection is not sufficient, however, to contraindicate it in many cases, for additional room can be obtained by resection of the last rib. So far as the writer is aware, laparotomy has never been performed for the simple removal of a calculus. Nephrectomy, or removal of the kidney, may be required for various conditions, among which is to be reckoned a renal calculus with pyelitis of sufficient severity to threaten life or give rise to constant suffering; but as it is often indicated for other reasons, its consideration will be deferred. Pyelitis may be excited by the presence of other foreign bodies, among which are coagula and parasites. An acute pyelitis may accompany an acute nephritis. Occasionally also an idiopathic pyelitis is said to be met with, but it must be difficult in such a case to exclude the presence of some irritant which has escaped observation. {53} Secondary Pyelitis. Pyelitis is most frequently excited by the propagation of an inflammatory process upward from the bladder, and hence it is, with its resulting effects upon the renal structure, one of the most important complications of chronic cystitis and of surgical affections in the lower urinary passages. Anatomically, a pyelitis of this character differs but little from that of local origin described above, except that the contents of the inflamed cavity do not include deposits of urinary salts unless such have been formed secondarily. It is, however, more likely to be severe, and especially to affect the true renal substance more rapidly and more seriously, and consequently to be attended with constitutional symptoms in an acute form. Two factors are of especial importance in determining the rate of development and severity of pyelitis supervening on affections of the urinary passages: First, the amount of obstruction which exists to the exit of the urine; and, secondly, the character of the cystitis as regards decomposition of the urine. It is obvious that whatever sends urine back into the ureters, or, what is the same thing, prevents its passage downward, will by keeping it longer in contact with the mucous membrane intensify whatever morbid action such an irritant would have, and of course a putrid or ammoniacal urine will induce inflammatory action, while a normal secretion might remain for a long time innocuous. Hence it is that we may have hydro-nephrosis and pyelitis entirely distinct from each other, but are very likely to have both combined in most cases.