From series 1 it is concluded that increases in pulmonary pressure improve the circulation in the embolic areas and that decreases in pulmonary pressure limit the circulation in the same areas. In this series the bronchial vessels showed no tendency to take up the circulation in the area of pulmonary embolism until the pulmonary pressure was as low as zero, and then only to a limited degree. It has been shown, however, that in the circulation of an entire lobe the fall to zero pressure in the pulmonary circuit is followed by almost complete taking over of the circulation by the bronchial arterial supply and the most reasonable explanation of why this does not occur when embolism is present in a smaller branch of the pulmonary is the inference that the physiological anastomosis between the two systems takes place in part before the pulmonary artery breaks up into branches small enough to be occluded by seeds of about three millimeters in diameter.

From series 2 it is concluded that although increases in pressure in the bronchial arteries cause somewhat greater inflow of bronchial injection mass into the embolic area, extremely high pressures are not sufficient to provide for complete circulation in the same district. This fact would tend to support further the belief that the anastomosis between the two vascular systems occurs before the smaller divisions of the pulmonary artery are reached.

From series 3 it is concluded that with a zero pressure in the pulmonary artery there is improved injection of the embolic area through the bronchial artery which is to be expected when it is remembered that zero pressure in the pulmonary artery favors a taking over of the circulation by the bronchial system. What pressure is found in the smaller pulmonary vessels is supplied by the bronchials. It has been shown that the anastomosis between the two systems probably occurs before the branches are reached which would provide lodgment for the turnip radish seeds. The pressure supplied by the bronchials would naturally be less beyond this point and hence the injection would be less complete in the embolic area than in the normal lung. This is shown to be the case by the results of the experiment.

From series 4 it is concluded that the absence of pressure in the bronchial circulation favors a better injection of the embolic area through the pulmonary vessels, which is to be expected when it is recalled that not until zero pressure is reached in the bronchial circuit does the pulmonary artery supply the bronchial vessels with blood.

Throughout the study it was found that whenever the two vascular systems were injected simultaneously the pleural vessels over the embolic area, as well as those over the normal lung, received their supply from the pulmonary vessels. When only one system was used for injection the pleural vessels over the embolic area showed about the same degree of injection as those of the embolic area itself.

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