180 CONTENTS OF THE CHEST. 



When the chest is opened soon after death, we recognize it in the steam that arises, 

 and in a few drops of fluid, which, being condensed, are found at the lowest part of 

 the chest. 



The quantity, however, which is exhaled from all the serous membranes, must be 

 very great. It is perhaps equal or superior to that which is yielded by the vessels 

 on the surface of the body. If very little is found in ordinary cases, it is because the 

 absorbents are as numerous and as active as the exhalents, and, during health, that 

 which is poured out by the one is taken up by the other; but in circumstances of dis- 

 ease, either when the exhalents are stimulated to undue action, or the power of the 

 absorbents is diminished, the fluid rapidly and greatly accumulates. Thus we have 

 hydrothorax or dropsy of the chest, as one of the consequences of inflammation of the 

 chest; and the same disturbed balance of action will produce similar effusion in other 

 cavities. 



The extensibility of membrane generally is nov^-here more strikingly displayed than 

 in the serous membranes, and particularly in that under consideration. How different 

 the bulk of the lungs before the act of inspiration has commenced, and after it has 

 been completed, and especially in the laborious respiration of disease or rapid exer- 

 tion! In either state of the lungs the pleura is perfectly fitted to that which ii 

 envelopes. 



The pleura, like other serous membranes, is possessed of very little sensibility. 

 Few nerves from the sensitive column of the spinal chord reach it. Acute feeling 

 would render these membranes generally, and this membrane in particular, unfit for 

 the function they have to discharge. It has too much motion, even during sleep ; and 

 far too forcible friction with the parietes of the thorax in morbid or hurried respiration, 

 to render it convenient or useful for it to possess much sensation. Some of those 

 anatomists whose experiments on the living animal do no credit to their humanity. 

 have o-iven most singular proof of the insensibility, not only of these serous mem- 

 branes", but of the organs which they invest, Eichat frequently examined the S])leen 

 of dogs. He detached it from some of its adhesions, and left it protniding from the 

 wound in the abdomen, in order "to study the phenomena;" and he saw "them teai 

 ino- off that organ, and eating it, and thus feeding npon their own substance," In 

 some experiments, in which part of their intestines were left out, he observed them, 

 as soon as they had the opportunity, tear to pieces their own viscera without any 

 visible pain. 



Although it may be advantageous that these important organs shall be thus devoid 

 of sensibility when in health, in order that we may be unconscious of their action and 

 motion, and that they may be rendered perfectly independent of the will, yet it is 

 equally needful that, by the feeling of pain, we should be warned of the existence of 

 any dangerous disease": and thence it happens that this membrane, and also the organ 

 which it^'invests, acquire under inflammation the highest degree of sensibility. The 

 countenance of the horse labouring under pleurisy or pneumonia will sufliciently indi- 

 cate a state of suffering ; and the spasmed bend of his neck, and his long and anxious 

 and intense gaze upon'his side, tell us that that suffering is extreme. 



Nature, however, is wise and benevolent even here. It is not of every morbid 

 affection, 'or morbid change, that the animal is conscious. If a mucous membrane is 

 diseased, he is rendered painfully aware of that, for neither respiration nor digestion 

 could he perfectly carried on while there was any considerable lesion of it; but, en 

 the other hand, we find tubercles in the parenchyma of the lungs, or induration or 

 hepatization of their substance, or extensive adhesions, of which there were few or 

 no indications during life. 



The pleura adheres intimately to the ribs and to the substance of the lungs; yet it 

 is a very singular connexion. It is not a continuance of the same orfranisation : it ir- 

 not an interchange of vessels. The organ and its membrane, ahhoufrh so closely 

 connected for a particular purpose, yet in very many cases, and wliere it woiild least 

 of all be suspected, have little or no sympathy with each other. Inflammation of tlu' 

 lunn-s will sometimes exist, and will "run on" to ulceration, while the pleura will be 

 very little affected : and, much oftener, the pleura will be the seat of inflammatior. 

 nnd will be attended by increased exhalation to such an extent as to suffocate the 

 animal, and yet the lungs will exhibit little other morbid appearance than that ol 

 mere compression. The disease of a mucous membrane spreads to other parts — thai 



