CALCULUS OF THE KIDNEY.
occasional passage of red sand from the bladder in childhood is not an uncommon occurrence. As a rule, little pathological significance is to be attached to it. Uric acid is very liable to be formed if food is taken largely in excess of the requirements of the system. It is not even neces sary that the food be nitrogenous to produce this result ; for as Dr. Garrocl has observed, it is a mistake to suppose that an animal diet mtist tend. more to the formation of uric acid than a vegetable one. It must be re membered, however, that the presence in the urine of a deposit of lithie acid or its salts is no proof that any excess of the acid is formed and se creted. The increase is often only apparent. When'the urine is scanty from deficiency of water, the uric acid may appear to be in excess. Again, great acidity of urine may cause a deposit of uric acid. The neutral lithates are more soluble than the acid lithates, and these than uric acid. Therefore, if the urine is full of neutral salts, any cause which will remove a part or the whole of the base will throw down a precipitate. The addi tion of acid will do this. Thus, if very acid urine be secreted into the bladder when this already contains a neutral or alkaline urine, the acid abstracts the base from the neutral salts and a deposit is formed at once.
The uric acid appears in the urine in the form of crystalline grains, or, if very abundant, as a red sandy deposit. In infants and young children there appears to be a special tendency to uric acid deposits ; and these may be thrown down in the kidney itself before the urine has passed into the bladder. The so-called uric acid infarctions of the kidney, forming yellowish red streaks running in the direction of the pyramids, may be found after death in the youngest infants—in them, indeed, more fre quently than in older children. These infarctions consist of amorphous urate of ammonia mixed with crystals of uric acid, and occupy the straight tubes of the pyramids. They do not, any more than the sandy deposits in the urine, indicate the existence of kidney disease. They are clue to ex
cessive feeding, or, in young babies, to the increased metamorphosis of tissue elements which must take place after birth in consequence of the newly-inaugurated processes of digestion, respiration, and generation of heat.
A deposit of crystals of uric acid may be formed at any part of the urinary apparatus. The urinary tubules often contain such collections. A. particle of crystallised uric acid is deposited in the cortical part of the gland. It may remain in this spot, or may pass further down the urinary apparatus into the straight tubes or the pelvis of the kidney. In either case it is apt to become enlarged by successive additions to the original nucleus. Great irritation is often caused by the passage of these frag ments, and even minute crystalline particles, if with sharp angles, may so scratch and wound the delicate membrane lining the fine tubules of the kidney and calices of the pyramids, as to be a cause of hemorrhage. In spite, however, of the frequency of sandy deposits, the urine in childhood does not, as often as might be expected, contain an admixture of blood. At least, an intimate blending of the blood with the urine, such as is known to be characteristic of renal haemorrhage, is in the child comparatively rare.
Besides uric acid, oxalate of lime concretions are not uncommon in children. These are dependent upon the same causes as the preceding. According to Schenck, uric acid is converted by oxidation into oxaluric acid, and this is readily decomposed by both acids and alkalies, splitting up into oxalic acid and urea. The oxalic acid at once combines with the base of any lime salt which may be present, and is precipitated as the insoluble oxalate of lime. This process may take place in any part of the urinary passages, and if crystals of oxalate of lime are found in warm urine before the fluid has had time to cool, it may be inferred that they have been formed inside the body, and we should think of the possibility of calculus.