RESPIRATION. 207 



or with diseased secretion, the respiration is heard with various 

 sounds, rough and snoring (sonorous rattle), shrill, squeaking, 

 chirping, hissing (sibilant rattle), gurgling (mucous rattle); and, if 

 too much fluid exists in their extremities or the air-cells, we hear 

 a crackling sound (crepitant rattle). If the tubes are quite ob- 

 structed, or the lung compressed by air or fluid in the pleura, or 

 by a solid, or if they are solidified, we hear no respiratory murmur. 

 In the three latter cases, the walls of the chest, when struck at the 

 spot affected, do not give out the hollow sound which the presence 

 of air in the lungs naturally gives, but are as dead as if any solid 

 muscular part was struck. These and many similar facts, dis- 

 covered by Avenbrugger h and Laennec, are of the highest utility 

 in detecting diseases of the chest, exist by physical necessity, 

 and, being facts, are just as important to the medical philo- 

 sopher as any other symptoms ; and though some, who have 

 contrived to acquire a name among the ignorant, may affect to 

 despise them, the rising generation feel justified in ascribing their 

 contempt to indolence, conceit, and ignorance an ignorance so 

 disgusting, that it must eventually reduce them to their proper 

 level. 



The elasticity and muscularity of the lungs are not sufficiently 

 great to expel the whole of their air in expiration. Thus they 

 remain constantly in a certain degree of distension. 



I now recur to the subject of the circulation of the blood, as 

 promised in the last chapter. 



The vacuum constantly threatening in the chest, according to 

 Dr. Carson, either from the shrinking of the lungs or the con- 

 traction of the inspiratory muscles, and, I may add, from the ex- 

 pulsion of blood from the ventricles of the heart, will evidently be 

 prevented, not only by the falling of the ribs and the ascent 

 of the diaphragm in the former case, and ingress of additional air 

 into the bronchise in the latter, but also by the flow of venous 

 blood into the auricles : for the venous blood, being subject to 

 the full atmospheric pressure without the chest, will necessarily 

 be driven into the chest to prevent a vacuum k ; the blood of the 



h Inventum novum ex percussione thoracis humani, abstrusos interni pectoris 

 morbos detegendi. 1761. 



' Reisseisen, 1. c. p. 23. 



k See Dr. Huxham. ObservationesdeAereetMorbisEpidemicis. Londini, 1751. 

 Prolegomena, p. 7. sqq. " Facto nempe in ductibus pulmonum sanguineis mo- 



p 2 



