Albuminuria of renal origin is due to passive congestion or to inflammation, except in certain anemias, cachexiae, and fevers, when the structural change in the kidneys is a degenerative one. It has been urged that in some cases the albumin of the blood was in unusual combination, so that elimination by the kidneys was possible, although these organs were not structurally changed, and the following facts have been advanced to sustain this view - namely, that raw egg-albumen introduced into the blood by intravenous or hypodermic injection, or even much of it by the stomach, provokes an albuminuria, while cooked egg-albumen does not do so when taken into the stomach. Although this observation may be correct, it is found, in practice, that whenever albumin is demonstrable in the urine either continuously or intermittently, there are structural changes in the kidneys. It escapes from the glomeruli with the water of the urine. If any finds its way into the tubules through their walls it is insignificant in amount, except when a hemorrhage occurs sufficiently great both to fill the interstitial spaces and to rupture some of the tubules. Therefore in the cases of albuminuria ordinarily met with, structural changes exist in the glomeruli.

As a rule, casts are found in urine when albumin is of renal origin. They are sometimes few in number as compared to the amount of albumin, but they can be found, being formed, within the tubules, of material secreted by or made from the epithelium. Epithelial cells, as well as blood-corpuscles, are often embedded in the casts, and still oftener the granular debris caused by their disintegration may be seen in them. Casts are very commonly met with when much abnormal fermentation occurs in the gastro-intestinal tract and when the liver is inactive. Albumin is not always found in these cases, although in most instances a trace of it can be demonstrated in the urine from time to time. Frequently also casts can be found in the urine before albumin appears, when there is slight chronic renal congestion. Toxins produced by gastro-intestinal indigestion cause casts to appear in the urine because the kidneys are irritated by them and the function of the epithelium is modified. Several glasses of beer, or equivalent quantities of other alcoholic beverages, taken at one time will cause casts to be formed, and for the same reasons. The fact that gastrointestinal indigestion at times causes slight transitory albuminuria is of importance as a guide to its prevention and treatment.

Albuminuria in febrile maladies is due in part to the presence of toxins in the blood, which must be eliminated through the kidneys, and in part to those structural changes called cloudy swelling, that are so common in these cases. Even in fevers regular and copious bowel movements are necessary to prevent albuminuria, as every watchful clinician has had occasion to observe. Casts become more numerous, more granular, and albumin is more constantly present when the intestines are clogged with fecal matter.

Abuminuria is aggravated not only by digestive disorders, but also by certain foods. Several raw eggs or a good meal of meat, especially such as is very rich in extractives, will usually increase the percentage of albumin in the urine. Mental and physical fatigue likewise aggravate albuminuria possibly by causing the rapid production of waste-products that must be eliminated by the kidneys.

Intermittent albuminuria and cyclic albuminuria are forms in which it occurs at regular or irregular intervals, but does not affect the general health of the patient. The amount of albumin voided is small. It is caused to appear either by physical exertion or by eating albuminous foods. To prevent the appearance of albumin in the urine in such cases it is not necessary, as a rule, to forbid its use altogether. It is possible to eat an amount, which must be determined by trial. Those cases in which physical exertion is the chief or only cause of albuminuria cannot be relieved very easily.

Certain nitrogenous foods are more likely than others to cause albumin to appear in the urine. Milk, although it contains from 4 to 5 per cent, of protein, is the food par excellence for those who have albuminuria. If eggs are eaten raw, albumin is more likely to appear or to be increased in the urine than when they are used after cooking. Fish and oysters affect only the severe cases unfavorably. The meat of squab and the breast of chicken are believed by many to be less harmful than the red meats, such as beef and mutton. Breads, cereals, vegetables, and fruits may be eaten by most of those having albuminuria. The use of these articles of food must be curtailed because of uremia, severe nephritis, or complicating disorders of digestion, not because of albuminuria.

Water and other permissible liquids should be drunk copiously, eight to twelve glasses daily, when casts, renal epithelium, blood-cells, or granular matter, as well as albumin, appear abundantly in the urine. As in such cases the urine is diminished in amount, diuresis must be provoked by drinking water freely. Milk also is almost a necessity in the treatment of these cases, both because it is a perfect food and because it is a diuretic of great value. Tea, coffee, and cocoa may be permitted in the mildest cases provided they do not hinder or disturb digestion. Alcoholic beverages must be forbidden when any portion of the urinary tract is inflamed or diseased, for they aggravate such conditions.

The details of dietetic treatment in the common cases of albuminuria can best be described in connection with the subjects of passive congestion of the kidneys and of nephritis.