SECRETION OF NITROGEN Inquiry into the conditions of nitrogen excretion can have no value unless it is combined with a study of tissue changes. The postulate here stated holds good also in regard to most of the other urinary ele ments, w hich are excreted, such as phosphorus, chlorine, calcium, and magnesium, and this fact has only recently found acceptance in pediatric re.search. Many examiners have concerned themselves with the study of the quantitative excretion of certain elements of the urine at particular ages, without taking any note of the supply of this element, and these examinations are valueless if we accept the postulate advanced in the opening sentence of this paragraph. The ordinary tabulation of the amount of urea-nitrogen excreted by children at various ages may therefore be omitted here. The values given teach nothing unless they are computed with reference to the total metabo lism. tinder normal physiological conditions, the quantity of nitrogen excreted will depend upon the supply- and upon the intensity of cell growth. The more active the cellular development, the more nitrogen will be retained. The character of nitrogen distribution is of great value in the physiology and pathology of the infant. It is well estab lished that in both infants and older children the greatest part of the nitrogen is eliminated in the form of urea, and that any other conclusion is the result of faulty methods.
The following table from Langstein and Steinitz demonstrates the distribution of the nitrogen in the urine of breast-fed and artificially nourished infants.
The quantity of ammonia, or the proportion of ammonia-nitrogen to the total nitrogen (ammonia cmfficient) is generally increased in acute disorders of nutrition of infants, while the quantity of urea is correspondingly diminished. This fact has assumed importance in the pathology of infantile metabolism because it shows tbat the alkalies excreted are not sufficient to neutralize the urinary acids (doctrine of acidosis, see pathology of metabolism). The nitrogen which cannot be precipitated by phospho-tungstie acid, and which cannot be trans formed into ammonia by heating with metaphosphoric acid, has been, of late years, called amino-acid-nitrogen. The school of Friedrich
Miller has emphatically and justly objected that this nomenclature is unsuitable, if for no other reason, because its results are founded upon an indirect method. Moreover, a considerable proportion of the nitrogen, which is not precipitated by phospho-tungstic acid, and which is not urea, is present in the form of hippuric acid in adults, but we do not as yet know the proportions in which these Substances exist in the urine of children. The condition, which has been applied in adult life, that the excretion of amino acids shall be accepted only when the quan tities have been directly proved, must hold good when we discuss the matter in connection with childhood.
Recent experiences have proven that under normal conditions, adults excrete amino acids, such as glyeocoll, but in ,Mfants the pres ence of this product of albumin-splitting has not yet been demonstrated (investigations by Rietschel at the Berlin Children's Clinic). It is true that there are two well-known disturbances of metabolism which occur in the infant, in which there appear in the urine amino acids or their derivatives: namely eystinuria, and alkaptonuria. The former, which is sometime:3 hereditary in origin, is generally manifested by thc ap pearance of a sediment consisting of hexagonal tables, which when examined prove to be cystin (aminothiopropionic acid). The crystals are chemically characterized as cystin by the fact that their solution will turn black when boiled with an alkali and lead aeetate (formation of sulphide of lead). In alkaptonuria, which is usually congenital (Garrod, Erich Meyer), a derivate of the aromatic plum of the albumin molecule, the so-called alkapton, secreted, which is characterized as hemogentisic acid (dioxyphenyl acetic acid). The presence of this acid makes the urine turn black when exposed to the air, a process which is quickened by the addition of an alkali (the mothers state that the urine leaves (lark spots upon the baby's napkins), and causes it to reduce alka line ammonia-silver solution when cold, and Fehling's solution when hot, and to turn green transitorily upon the addition of ferric chloride.