DYSPNCEA. 485 



element (the red corpuscle] and its circulation, or (2) the nervo- 

 muscular apparatus, including the lungs and air-passages, the 

 respiratory centre, and the afferent and efferent channels of 

 communication. The first class were discussed in chapters viii. 

 and ix. ; the second will now be briefly noticed. 



Circulatory, inflammatory, and degenerative changes com- 

 prise a large part of the diseases of the respiratory organs, such 

 as bronchitis, pulmonary congestion, emphysema, and pleurisy, 

 to which must be added new growths, whilst tuberculosis and 

 syphilis occupy an intermediate position. Whatever their 

 pathological nature, these diseases produce certain well-marked 

 anatomical changes in the parts. The passages may prove to 

 be obstructed, or actually occluded, by swelling of their 

 mucosa, and by various products, such as mucus, pus, blood, or 

 debris, which may be retained, inspissated, or possibly decom- 

 posed, thus irritating the nerves and vessels. Some of the 

 bronchia may be entirely blocked, with collapse or consolida- 

 tion of the corresponding lobules, and disturbance of the air 

 pressure (emphysema) and blood pressure (hyperaemia) in the 

 parts around. Portions of the lungs may be found either con- 

 solidated by pneumonia, or compressed by pleurisy, airless and 

 functionless. Tracts of various size are frequently entirely 

 destroyed by phthisis or gangrene. Haemorrhage may occur in 

 the alveoli or passages. The right heart frequently proves to 

 be secondarily enlarged, from disturbance of the venous cir- 

 culation, the viscera congested, and the serous cavities and 

 extremities dropsical. 



Whilst many of these anatomical changes are fortunately 

 remediable, others are not so, and the efforts of the practitioner 

 can only be directed to the relief of their symptoms, or, more 

 correctly, their effects. Amongst these, disturbances of re- 

 spiration, spasm, cough, expectoration, vomiting, and pain, 

 alone require to be briefly noticed here. 



Dyspnoea is a natural effort to increase oxygenation, and 

 is due to stimulation of the respiratory centre in two distinct 

 ways, viz. (1) by the imperfectly oxygenated blood circulating 

 within it, and (2) by exaggeration of the impressions coming 

 from the air passages and lungs. Obviously these two sets of 

 causes are usually combined, since such anatomical changes as 

 have been mentioned, interfere at the same time with the proper 

 contact of the air and blood in the lungs, and irritate the pul- 

 monary branches of the vagus. As a rule, dyspnoea is successful 

 and highly beneficial ; but unfortunately, if it fail to give 

 relief, it tends to aggravate the distress. 



Spasmodic dyspnoea, commonly called " asthma," is referable 

 to sudden intermittent irritation of the vagus or centre. 



