TO EXTRA-UTERINE LIFE In the first days of its life the infant passes but little urine; the scanty ingestion of fluids and the active loss of water through the skin and lungs reduce the kidney-secretion to a level lower than that cor responding to the body weight. Regular examinations of the urine show the striking fact that albumin is present. for one or more days in the urine of at least one half of all newborn infants and according to the latest investigations in all. This albumin is nucleo-albumin; more rarely some other proteid substance (Flensburg). The assumption that mucin is present in the urine of newborn children (Cruse) has not been substantiated. The amount of albumin varies but is never large. The excretion of albumin begins after birth (urine found in the bladder at birth is usually free from albumin), lasts rarely only one, usually the first four days and is, as a rule, ended within the first nine days of life (Cruse). In Very rare cases it has been known to persist as long as the second month of life.
The cause of this albuminuria has not been definitely settled. it possibly has a connection with infarction of the kidney in the newborn (Hofmeister); at least it is true that the height of the infarct formation is often accompanied by considerable albuminuria (Flensburg). The absence of urates does not argue against this, since infarctions may be present in the kidney without there being anything demonstrable in the urine. With this assumption as a basis one could attribute the nucleo albumin of the newborn to some damage to the parenchyma of the kid ney- by uric acid infarction. Nucleo-albumin does not come from the blood, since none is present. there; it has its origin in the cells of the parenchyma of the kidney. The question, whether albuminuria in the newborn is a physiological process which, according to Virchow, depends on revolutionary changes in the metabolism of the newborn at the moment of birth, remains, according to Czerny and Keller, as yet undecided.
The urine of the newborn is clear, immediately after birth; later, however, it usually is cloudy and remains so for 4-5 clays. Microscopi cally the urinary sediment shows the presence of pavement epithelium from the peripheral urinary passages, also leucocytes, hyaline and epi thelial casts, renal epithelium and amorphous hyaline substance (Cruse, Flensburg). According to Reusing, casts are present in the urine of 39.4 per cent. of breast-fed children and only 9.1 per cent. of artificially fed children. This is connected with the larger ingestion of fluids by the children fed on eow's milk, who thus secrete a less concentrated urine which is less damaging or irritating to the kidney epithelium.
Finally a brick-red sediment appears in the urine, often even on the first day, but usually on the second to the fourth, which according to Flensburg has been analyzed by Sjoqvist and found to be composed of urate of ammonium; with a hyaline substance for a. nucleus it gathers in rods or balls and often contains incrusted epithelial cells or casts_ Thissediment owes its origin to the laic acid infarctions of the newborn. It is only excreted during the first days of life, usually from the second to the fourth day and rarely later than the beginning of the second week. According to Flensburg these infarcts are present in all newborn children. Where they are present in considerable proportions brick red spots are seen on the diaper of the child; retention of urine in the newborn seems sometimes to be connected with the elimination of infarctions. In this case the first urine is voided without diffi culty, but later retention and restlessness set in and may persist for many hours.
Uric acid infarctions are rarely found in the kidneys of still-born infants. In children who have lived for a time, however (hours, days or weeks), one exceptionally often finds that the pyramids alone of the kidney are striped with a large number of reddish- or brownish-yellow, often also light yellow lines; under the microscope these turn out to be balls, granules or rods of uric acid salts embedded in an organic, pro teid-like substance. Virchow considered the urate to be the ammonium salt. The occurrence of these infarcts has not yet been explained. It is true that Reusing, Sjoquist and others have established the very high percentage of uric acid in the urine of the newborn; since however, in adults with very high percentages of uric acid, e.y. in cases of leukemia, infarctions have never been described; it becomes necessary to assume other peculiar relations in order to explain the infarct formation. Flens burg believes that. a proteid-like substance is secreted in foetal life and during the first days after birth, which gathers in the convoluted tu bules, interferes with the passing off of the urine and becomes incrusted from the passage of the urine rich in uric acid. Spiegelberg was able to show that uric acid infarctions follow the injection of orates in new born animals but. never in adults. The explanation of this was not forthcoming from his researches.