In pregnancy the kidneys always give evidence of a constant congestion, and the chief symptom of this is the great quantity of renal epithelium shed with the urine. This engorgement has given rise to the term "kidney of pregnancy." There has been much discussion of this condition, especially as to the possibility of differentiating it from beginning nephritis. In 227 consecutive cases of pregnancy in which the urine was examined at short intervals by myself throughout the entire gestation, there was always an enormous quantity of epithelium, and this presence of epithelium is so constant that its absence is a proof that pregnancy does not exist. It is as physiological as any other somatic change in the puerperium. Von Leyden and other German observers look upon the degenerative alteration in the epithelium of the renal tubules as pathological, but apparently more definite symptoms are necessary to make a diagnosis of significant nephritis. Williams[118] says that in the examination of 1000 pregnant women at Johns Hopkins Hospital in Baltimore traces of albumin were found in 50 per cent. without subsequent serious disturbance, but where considerable albumin with casts other than hyaline was seen there were symptoms of toxemia later, and several of these went on into eclampsia. Fisher[119] held that red blood-corpuscles in these cases indicate acute nephritis; and granular and epithelial casts, chronic nephritis. Like the Johns Hopkins cases, he found albumin in 50 per cent. of his patients. Albumin in slight quantities is found to be extremely common toward the end of pregnancy. Meyer,[120] in an extensive study of the kidney in pregnancy, made at Copenhagen, found albumin in 5.4 per cent. of the women. During the last month of gestation 71 per cent. of the women showed albumin. Premature births occurred in 8 per cent. of the patients who had had albuminuria, but in 21.5 per cent. of the women who had had casts. Delicate tests for albumin are used by men who find these high averages, as a few leucocytes from leucorrhoea will give the reaction. Most of these cases have no clinical significance. [118] _Obstetrics_, p. 456. [119] _Praeger medizinische Wochenschrift_, 1892 n. 17. [120] _Zeitschrift für Geburtshülfe_, bd. 16, n. 2. It is usually impossible to differentiate in pregnancy a lighting up of an old nephritis from a toxemia. Where there is a history of nephritis before the pregnancy, this often clears up the diagnosis. Nephritis is likely to manifest itself in pregnancy earlier than toxemia; albuminuric retinitis is commoner in nephritis, but these facts are no real help in differentiation. The position of the uterus may be a cause of nephritis, according to the _American Text-Book of Obstetrics_; but De Lee and others hold that the growing womb cannot possibly be a cause. Many other origins have been suggested, but without sufficient proof.