HYFEILEMJ.A OF THE LUNG. 135 



mere augmented action of the heart does not produce hyperaemia. The 

 fuller the arteries, and the more distended their walls, so much less full 

 are the veins, and so much is the tension of their walls lessened. The 

 efflux from the capillaries is accelerated in proportion as the afflux is in- 

 creased ; the circulation is quickened without any actual increase of the 

 quantity of blood in any of the organs. Whether another condition 

 exists in the lungs, or whether increased heart-action alone is thus capa- 

 ble of giving rise to hyperaemia, we do not attempt to say, as we are 

 not sufficiently acquainted with the normal condition of the pulmonary 

 circulation, and even the natural degree of pressure of the blood in the 

 pulmonary artery when the chest is closed is unknown to us. 



2. The instances of fluxion to the lung produced by direct irritation, 

 >y the transitory action of cold upon the pulmonary tissue, the inhala- 

 tion of very hot air, or of air mingled with irritating matter, are easier 

 of comprehension. Here the tissue in which the capillaries are im- 

 bedded seems to be relaxed, and to oppose less resistance to the relaxa- 

 tion of the capillary walls. The same causes, acting upon the skin, pro- 

 duce fluxion upon it in a manner quite similar. The skin reddens if it 

 be exposed to cold for a short time, as if a hot poultice or a sinapism had 

 been laid upon it. The chronic fluxions, too, which accompany the for- 

 mation and softening of neoplastic growths and tubercles, especially 

 tuberculosis of the lungs, occur in the same way, and may be traced to 

 abnormal relaxation of the connective tissue. 



3. A third form of fluxion, as yet far too little noticed, but which 

 we have already alluded to in treating of emphysema and pulmonary 

 compression, occurs in all cases of obstruction of the pulmonary circula- 

 tion from stasis in its capillaries, or where the latter are compressed or 

 destroyed, and, of course, it must develop in portions of the lung where 

 the circulation is free from impediment. Such collateral fluxion is a 

 physiological sequel to ligation of an arterial trunk, as is proved by the 

 appreciable dilatation of the surrounding unobstructed vessels, and it is 

 quite indispensable to the symptomatology of most diseases of the lung. 

 In the most simple manner it explains symptoms, which otherwise would 

 be unintelligible, and it accounts for the action of venesection in pneu- 

 monia, pleuritic effusion, etc. 



4. Finally, we have already stated that a rarefaction of the air in the 

 alveoli produces determination of blood to the lungs, just as a cupping- 

 glass or the boot of Junod causes fluxion to the skin. The suspended 

 or diminished pressure to which the capillaries of the air-cells of a child 

 with occluded glottis are subjected, when it expands its chest, is, as we 

 have seen, the main reason for the consecutive bronchial catarrh and 

 pulmonary oedema in croup, and of the poor success of tracheotomy. 



TI. Stagnation of the blood, passive hypercemia, from which we 



