It is necessary to distinguish, first of all, between an essential and an accidental albuminuria, the first referring to that condition where the albumen is secreted with the urine and forms an essential part of it, and {38} the other to the accidental admixture from the presence of pus or blood, which may have made its appearance at any point below the secreting tubes. When hemorrhage takes place from the kidney, albumen is of course present in the urine, but its signification under these circumstances is entirely different from that which it bears when unaccompanied by the corpuscular elements of the blood. No means at present exist for determining whether a small amount of albumen present in the urine is more than enough to be accounted for by the pus or blood known to exist by the presence of its corpuscular elements or of its coloring matter. An approximate estimate may be made by one familiar with such examinations, but no rule can yet be laid down. Such a rule might be approximately established by a succession of counts with the hæmocytometer of the corpuscles found in albuminous urine of known percentage, or estimates of hæmoglobin by color tests. The exact conditions of the kidney or of the blood which may cause the appearance in the urine of albumen without blood or pus--that is, of true albuminuria--have been the subject of much experiment and argument, which it would be impossible to reproduce, even in outline, within the limits of this article; and this is the less to be regretted since they have as yet led to no practical or generally accepted conclusion. A few of the more important facts bearing on the question may, however, be stated here. Albumen other than serum-albumen, when introduced into the circulation either by injection into the veins subcutaneously, or if in very large quantity by the mouth, is rapidly excreted by the kidneys. This albumen also, if collected from the urine of the first animal and injected into the vein of a second, again comes through the kidneys. The albumen, however, which is obtained from the urine of an ordinary case of albuminuria--that is, serum-albumen--does not behave in this way, but is not excreted through healthy kidneys. These facts seem to show that the appearance of albumen in the urine in ordinary cases of renal disease is not to be attributed to any change in its quality approximating it to egg-albumen, for instance, but is due to the condition of the kidneys. Disturbances of the renal circulation, especially those giving rise to venous stasis, are very likely to cause albuminuria; a temporary ligature of the renal vein causes albumen to appear in the urine after its removal, and ligature of the ureter has the same effect.