Ventilation standards for small mammals have been prepared on the basis of the relationship between alveolar ventilation and metabolism. On the assumptions of an average respiratory quotient of 0.85 and physiological dead space directly proportional to tidal volume, the relationship between tidal volume, breathing frequency, and body weight has been derived. The standards are presented in a graphic form and as a slide rule. animal ventilation; artificial respiration; tidal volume, breathing frequency and body weight relationship Submitted on August 15, 1963

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SUMMARY1. Glomerular blood flow distribution was studied in seventy-eight new-born mongrel dogs aged 1-40 days by measuring the distribution of radioactive labelled microspheres within the kidney.2. The microsphere technique was found to be a valid indicator of glomerular blood flow distribution for the new-born dog since (a) the spheres were completely extracted by the kidney, (b) more than 95 % of the spheres were trapped in glomerular capillaries, (c) the spheres were evenly distributed within any specific region of the kidney and, (d) the spheres did not interfere with renal haemodynamics.3. Plasma flow per gram tissue to inner cortical glomeruli, relative to that to outer cortical glomeruli, the IC/OC flow ratio, was high at birth, decreased over the first 2 weeks of life and remained relatively constant thereafter. Plasma flow per gram tissue to the outer cortex increased over the whole 40 day period while that to the inner cortex decreased slightly and then increased after 2 weeks.4. The IC/OC flow ratio decreased in a curvilinear fashion as blood pressure rose with maturation. Acute increases or decreases in blood pressure in any animal produced decreases or increases, respectively, in the IC/OC flow ratio.5. There was no correlation between the IC/OC flow ratio and renal extraction of p-amino-hippurate (EPAH)-6. There was histological evidence that glomerular differentiation persists for 2 weeks during the post-natal period in the dog. This continuing post-natal glomerulogenesis takes place only in the outer cortex.7. These results are consistent with the hypothesis that an important factor in renal maturation is a redistribution of blood flow within the kidney. As the animal matures a greater fraction of the total glomerular blood flow goes to outer cortical glomeruli. This is due partly to the 92 LEONARD I. KLEINMAN AND JOHN H. REUTER continuing glomerular differentiation taking place in the outer cortical region and partly to the increasing arterial blood pressure occurring with maturation.

SUMMARY1. The maturation of glomerular filtration rate was studied by comparison of thirty-six new-born mongrel dogs aged 1-35 days with six adult dogs.2. Under mannitol diuresis, glomerular filtration rate (GFR) rose from 0X 16 ml. min-'. g kidney-' at 1 day of age to 0 34 ml. min-'. g kidney-' at 1 month of age. Adult GFR averaged 0X68 ml. min-'. g-. There was good correlation of GFR with arterial blood pressure (r = 0-76, P < 0-001). Part of the statistical correlation of GFR with blood pressure was found to be independent of the relationship between blood pressure and age.3. Acute increases or decreases in blood pressure resulted in parallel changes in GFR in the puppies. There was no change of GFR with change of blood pressure in adult dogs. Carotid artery clamping, independent of blood pressure changes, produced increased renal vascular resistance and decreased GFR in the pups.4. Renal plasma flow (RPF) increased from 0 70 ml. min-'. g-' at 1 day of age to 1 80 ml. min-. g-1 at 1 month and showed good correlation with blood pressure (r = 0-67, P < 0-001). Filtration fraction (GFR/RPF) and renal vascular resistance did not vary with age in the pup and were the same as those for the adult.5. These results support the hypothesis that maturation of GFR and RPF are closely related to maturation of arterial blood pressure in the mongrel dog. The factors other than blood pressure which also affect renal maturation in the dog still need to be more clearly defined. LEONARD I. KLEINMAN AND RONALD J. LUBBE

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