The excretion of uric acid, which results essentially from the trans formation of the nuclein of the cell-nucleus, is tolerably constant in quantity during the first days of life. Reusing gives the following average figures for the absolute quantitative excretion of uric acid during the first (lays after birth:— It is of interest that in the urine of the newborn there may be found a substance which is closely related chemically to uric acid:— allantoin.
We are indebted to Goppert for a comprehensive study of the uric acid excretion of older children. His results show that it is at present impossible to fix a rule for different ages. Whenever we attempt to draw conclusions from the quantity of excreted uric avid, we must at thc same time take cognizance of the cliet and of the amount of total nitrogen. It may be stated, by the way, that children from one to two years excrete approximately 0.1 to 0.2 Gm. (1-3 gr.) of uric acid per day (on a mixed diet); from 2-5 years 0.2 to 0.1Gm. (3-6 gr.): and that the excretion will keep within these limits until the age of puberty.
The following table, taken from Czerny and Keller's Handbook, gives a good summary of the relative proportions of the nitrogen-contain ing substances in the urine up to the age of puberty:— Creatinin has not been demonstrated in the urine of healthy milk fed babes, but in febrile diseases it may appear, and also when intro duced into the system by mouth.
The proportion of carbon to nitrogen is relatively higher in infancy than in adults. While in adults, the carbon-nitrogen quotient will be found to vary between the figures 0.5-0.7, in infancy this ratio may reach 1.0 (Hubner, IIeubner, van Ordt). It has been inferred from this that in the urine of infants combinations of carbon and nitrogen are to be found in abnormal quantities, but this supposition is wrong, because the investigations of Steinitz and I.angstein have shown that the proportion of carbon to nitrogen is to a remarkable extent subject to alimentary influences, The smaller the absolute quantity of ex creted nitrogen, the higher is the quotient of carbon to nitrogen, and vice versa.
The proportions of chlorine, phosphorus, sulphur, calcium, and magnesium excreted have no interest a.side from the theory of metab olism. Therefore only a few points will be mentioned here. The
amount of chlorine excreted is in the first place influenced by the chlorine supply. The sound organism (or the healthy kidney) answer promptly to an over-supply by a more active excretion. Retention for more than a brief period points to pathological conditions. The importance of retained chlorides as a factor in (edema will be considered in the chapter on nephritis.
Still more complicated are the proportions of phosphorus, calcium, and magnesium. On the whole, the law holds good that the artificially fed baby excretes more phosphoric acid than the nursling. This differ ence is shown not only by eonsideration of the acutal figures, but by the proportion of phosphorus to nitrogen. This proportion is in nurs lings as 1 is to 7; in artificially' nourished infants as 1 is to 2. The quantitative estimation of the phosphates and of the total phosphoric acid is of importance, since their proportion is the measure of the acidity of the urine. According to Keller, the quantity of phosphorus con tained in organic combination is absolutely smaller than in adults. A summary of the phosphorus excretion of infants is found in the follow ing table, which recognizes the results of Keller's experiments.
The literature on the subject of the excretion of phosphorus in the urine i8 still too meagre to permit of any definite conclusions. The so-called phosphaturia, which has been more thoroughly elucidated by the work of Soetbeer, Tobler, and others, may be briefly considered. This is a disturbance of the phosphoric acid excretion in elder chil dren, and appears itself in the form of milky, turbid urine, which is cleared up by the addition of acid, and is therefore due to the presence of phosphates. Soetbeer has demonstrated that the primary cause of this disturbance is an excessive excretion of calcium by the kidneys taking Oil vicariously the function of the intestines, which may bc disturbed by some morbid process. The basis of phosphaturia is, there fore, a calcarinuria. Owing to the lack of a sufficient number of reports upon the subject the excretion of the alkali salts has not yrt been de termined accurately enough in healthy children to be discussed.