Gusserow claims, that since there must be in the fcetus an exchange of nutritive materials and activity of function, after the obliteration of the allantois at the second month, the urine must dow into the liquor amnii; and urea and ammonia, absent at first, increase in quantity in the liquor amnii as pregnancy progresses. The amniotic fluid is thus a fcetal secre tion.
That the fcetus does secrete urine is incontestible, and, as Bar has re marked, may be demonstrated in three ways: 1st. By anatomical observa tion, showing that the kidneys function:LW normally during uterine life, since urine Is almost always found in the bladder at birth; 2d. By patho logical observation, which teaches us that, when there is obliteration of the urinary passages, hydronephrosis of greater or less extent occurs. The kidneys are normal, save where modified by the pathological process, and the liquid contained in the urinary passages has the chemical com position of urine. If, in these cases, the amount of liquor amnii is not. diminished, it is simply because the excretion of urine is not the only source of the liquor amnii. Finally, uric acid infarctions have been found in the kidneys of infanbs. 3d. By experiment, Fehling, Gusserow and others have shown that certain medicines either absorbed by the mother, and thus passing through the placenta, or injected directly under the foetal skin, could be refound in the urine of the foetus; 4th. By the chemical. composition of the liquor amnii.
Prochownick has studied the chemistry of the fluid, and has proved the presence of urea, and concludes that the liquor amnii is an exclusive ly fcetal product, and is derived from the nutritive materials of the fcetns. The quantity of urea should therefore be proportionate to the energy of nutritive interchange. In point of fact it increases largely as pregnancy advances, and the kidneys begin to functionate. Ile therefore concludes: 1st. The liquor amnii always, after the sixth week of pregnancy, contains urea; 2d. It is produced by the skin and kidneys of the fcetus; 3d. -The quantity of urea during the last third of pregnancy is proportionate to the length and weight of the fcetua In a second chapter he proves that the liquor amnii contains chloride of sodium, and from a quantitative analysis of the liquor amnii, he con cludes: 1st. 'Uhe liquor amnii is exclusively a fcetal product, and is the product of the interchange of fcetal nutritive materials; 2d. It is secreted
by the skin and the kidneys, 3d. The secretion by the skin begins early in pregnancy; that by the kidneys commences only at its middle; 4th. The amnion is a serous membrane, and can absorb; 5th. This absorption becomes more and more easy as pregnancy advances; 6th. The concentra tion of the amniotic fluid increases during the first half of pregnancy, decreases rapidly at its middle, and thus remains about the same until its termination; 7th. The amount of the fluid at various times will be noted later.
Fehling holds that the albumin in the liquor amnii precludes the pos sibility of ita being a purely urinary secretion, since there is none in the urine of living children, and that there is no more urea in the fluid of the amnion than in other serous fluids.
c. The liquor amnii is due to a tranzudation of the fluid portions of the blood through the amniotic membrane.
Both Monro and Lobstein have seen fluid percolate through the inter nal surface of the amnion after injecting hot water into the umbilical arteries; and Jungbluth has found a minute capillary net-work, which he calls the vasa propria, in the superficial placental layer nearest to the am nion, which is almost always obliterated in the later months of preg nancy. This he c,onsiders as the source of the liquor amnii, and hence it is that that fluid is nearly identical with blood serum in composition. An excess of presaure in the fcetal circulation will cause a transudation in to the amniotic cavity from this capillary plexus, although of course, when we consider the length of the cord and the multiplicity of its spirals, the arterial pressure can be but feeble.
Gassner considers Jungbluth's explanation as only partially sufficient, since the liquor amnii increases during the second. half of pregnancy, when this capillary plexus has been obliterated. The fcetal urinary se cretion explains its continued increase, am' explains the cause of Gassner's law, that the quantity of the fluid is proportional to the weight of the fa3tus. Thus the relative quantity of albumin decreases in the urine diluted fluid, and therefore, in cases of occlusion of the fcetal urinary passages in the later months of pregnancy, the liquor amnii is absent or nearly so. But while Jungbluth's theory will explain certain cases of dropsy of the amnion, there are others that it will not explain.