The APS Journal Legacy Content is the corpus of 100 years of historical scientific research from the American Physiological Society research journals. This package goes back to the first issue of each of the APS journals including the American Journal of Physiology, first published in 1898. The full text scanned images of the printed pages are easily searchable. Downloads quickly in PDF format.
Do the controls of breathing differ with age? Pulmonary ventilation was measured by body plethysmograph and pressure transducer. After birth, breathing was irregular (pneumotaxic); steadiness from breath to breath was gained at 3 days; extraction of oxygen from the inspired air became more uniform after 10 days. In pO2 20–40 mm Hg only infants survived a half hour; ventilation did not usually increase, and often decreased. Hyperventilation even in 40 mm Hg was not sustained for many minutes in the newborn, but by 6 days was large and enduring. Heartbeats decreased in frequency during severe hypoxia. Oxygen consumption decreased 75% during hypoxia that allowed survival of infants; it sometimes recovered only slowly after hypoxia ended. Tolerance of infants to low oxygen thus consisted in ability to utilize some oxygen at low pressures and to dispense with some oxygen. Some factor other than pCO2 or pO2, possibly centrogenic, often controlled ventilation in infancy. Low oxygen maximally accelerated the breathing at an age when endurance of hypoxia remained. Submitted on May 12, 1960
Is fetal plasma a transudate of maternal plasma? Cl, Na, and K concentrations were measured in plasmas obtained by cardiac puncture of exposed rat fetuses while the maternal rat was under pentobarbital anesthesia. At rest, Cl had 0.95 x the maternal concentration, Na 1.00, and K 1.6x. When hypertonic NaCl was infused into a maternal vein, the Cl in the fetal plasma increased only half as much as in the maternal plasma, a steady differential being maintained at 1–3 hr. In contrast, Na increased alike in both plasmas. When electrolytes were depleted from the mother by intraperitoneal dialysis, both Na and Cl were lost proportionately. Sucrose solution added to the mother's blood diluted the electrolytes of her plasma but increased them in the fetal plasma by withdrawal of water. Analysis of the fetuses showed that water moved out from the fetuses while Na and Cl moved inward after NaCl was given to the mother; depletion of the mother led only to movement of Na and Cl from the fetus. Thus Cl and K are maintained in fetal plasma, when sampled in the above manner, at concentrations differing from those of maternal plasma; and circumstances were found in which these differences are exaggerated. Therefore fetal plasma is not a transudate.
Urine flow was measured in newborn and adult rats, urine being collected by means of a small plastic tube surgically inserted into the urinary bladder through the ventral body wall. Epinephrine in subcutaneous doses of 0.3 or 0.6 mg/kg of body weight produced a prompt diuresis which was nearly identical at all ages (1/4, 2, 6 days after birth; and adult). Arterial blood pressure was low in infant rats and was not increased by this dose of epinephrine. When infant rats breathed air low in oxygen (pO2 = 38 mm Hg), prompt oliguria lasted one-half hour; primary diuresis followed; secondary diuresis suddenly developed whenever ordinary air was again supplied. Within 15 days after birth the oliguria and the secondary diuresis were lost; primary diuresis appeared earlier and lasted a shorter time. Whereas rats up to 39 days after birth did not respond to pO2 of 56 mm Hg, adults responded to it with primary diuresis only. The urine produced during infant diureses was dilute as measured by chloride and refractive index, and remained acid. Pitressin did not interfere with these diureses. Adrenalectomy did not prevent the secondary diuresis. Though responses to epinephrine and hypoxia materialized at birth, their amount and character shifted with age, representing the terminal stages in fixiaton of a regulation.
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