I N PRELIMINARY studies to assay the effects of repeated long-term stimula-tion of cerebral autonomic centers, pentylenetetrazol (Metrazol) given intravenously or intramuscularly evoked predominantly generalized vasopressor responses in cats and one of the most consistent concomitants of this repeated vasopressor response in the cat was hypertrophy and hyperplasia of the pulmonary arteries. 15 In these chronic experiments, examination of the blood showed a notable increase in count of the red blood cells, and it was speculated that this condition might resemble the clinical entity of Ayerza's disease (pulmonary arteriosclerosis with polycythemia). A review of the literature reveals several reports of experiments on laboratory animals in which an erythrocytosis or reticulocytosis resulted from direct physical stimulation of the brain or ablation of cerebral areas. Schulhof and Matthies 22 injected sterile siliceous earth in the region of the hypothalamus of rabbits to cause a sterile inflammatory reaction simulating an encephalitis. Three of their animals showed an increase in count of the red blood cells of 1 to~ million. Dockhorn 6 produced a reticulocytosis in human subjects by the application of diathermy to the brain stem. Mettler 17 found a reticulocytosis of 0.3 to 7.4 per cent in dogs following bilateral frontal lobectomies and no such response was seen after a bilateral occipital lobectomy.

There is a wide range of normal counts of red blood cells in cats and dogs. Trautmann and Fiebiger 26 gave values of 7.~• 1 million cells per c. mm. for the cat and 6.1• 1 million cells per mm. for the dog. A major cause of polycythemia in animals is exposure to high altitude, and the degree of polycythemia depends upon the severity of hypoxia and the duration of the exposure. It is of particular interest to the present study that this type of polycythemia disappears after cervical transection of the spinal cord2 The present experiments were undertaken to determine, first, whether the medial hypertrophy and hyperplasia of cats' pulmonary arteries, pre-