Macklin and Macklin 245 



and the discovery of the origin and ramifications of PIE was at first incidental; 

 but the leads were quickly followed up, and what was initially a by-product 

 became one of importance. There were two series: (a) local and (b) general 

 overinflation of the lungs. 



Forcible Overinflation of Part of a Living Animal's Lung.—Some thirty-five 

 animals were used, mostly cats. A flexible male urethral catheter, with the end 

 cut off, was passed down the trachea of the anesthetized animal and as far as 

 it would go without effort into the bronchus of the right lower lobe, which it 

 entered naturally. The lung tissue about the tip of the catheter was then in- 

 sufflated with pure air blown into it from the mains of the building. In the 

 first cats used, the air contained the fumes of osmium tetroxide, but this made 

 no essential difiierence. The pressure varied from i to 22 mm. of mercury as 

 read on a manometer, but must have been somewhat higher than that to which 

 the alveoli were subjected. In most cases the abdomen and thorax became 

 swollen, and also the neck, axillae and chest if the insufflation was continued. 

 The efi^ect was very striking. It was usual to find a double pneumothorax. 

 Large air blebs were conspicuous in the axillae and retroperitoneum.^ The 

 heart was surrounded by bubbles. In the fresh condition bubbles could be seen 

 in the lung roots, and, by probing from the heart it was found that these were 

 in the sheaths of the pulmonary blood vessels. Examination of gross slices and 

 microscopic sections of the lungs, fixed by intratracheal injection, disclosed 

 air bubbles along the sheaths of the pulmonic blood vessels and in the tissue 

 extending out from these. The bubbles were small at the periphery of the lung, 

 where the vessels were small, and increased in size toward the hilum. The 

 appearance of the pulmonic vessels was indeed striking. The walls were col- 

 lapsed, and might even be folded inward upon themselves until in many cases 

 there was no discernible limien. Between this collapsed tube and the surround- 

 ing lung alveoli was a large space occupied by air (or by a space which had 

 formerly contained air when this had been given up in the technical manipula- 

 tions), and this space was crisscrossed by delicate cobweblike strands, the 

 remains of the connective-tissue sheath of the vessel. Looked at lengthwise 

 in gross pieces, with a low-power lens, the vessels often appeared as mere 

 crumpled tubes swung by tenuous guy ropes attaching in all directions, and 

 surrounded by bubbles. A glance would convince anyone that little or no 

 circulation could go on in such vessels. In one such case from an overinflated 

 excised calf lung, fluid could not be forced through at a pressure of three feet 

 of water. One could readily see why cyanosis should be a prominent feature 

 of airblock. A similar occlusion of pulmonic blood vessels was found in the 

 lungs of two children, one of whom had died after aspirating peanut frag- 

 ments,^' and the other of atelectasis of the newborn.^" 



The alveolar-base rupture points are invisible in ordinary histological sec- 

 tions, made from immersion-fixed blocks, but in certain of these animals their 

 sites were located by a method of injection of the previously overinflated lobe, 

 through the same bronchus, with hot gelatin containing minute carmine par- 



