ACTION OF THE LUNGS IN RESPIRATION. 581 



cera, and depress the ribs; in the latter movement they are aided by the 

 Longissimus Dorsi, Sacrolumbalis, &c., and also by the elasticity of the car- 

 tilages of the ribs, with that of the air-cells and air-tubes themselves. 



762. It is difficult to form an estimate by observations on one's self, of the 

 usual number and degree of the respiratory movements; since the direction of 

 the attention to them is certain to increase their frequency and amount. In 

 general it may be stated, that from 14 to 18 alternations usually occur in a 

 minute; of these the ordinary inspirations involve but little movement of the 

 thorax ; but a greater exertion is made at about every fifth recurrence. The 

 average numerical proportion of the respiratory movements, to the pulsations 

 of the heart, is about 1 to 5 or 4 ; and when this proportion is widely de- 

 parted from, there is reason to suspect some obstruction to the aeration of the 

 blood, or some disorder of the nervous system. Thus in Pneumonia, in which 

 a greater or less amount of the lung is unfit for its office, the number of respira- 

 tions increases in a more rapid proportion than the acceleration of the pulse; 

 so that the ratio becomes as 1 to 3, or even 1 to 2, in accordance with the de- 

 gree of engorgement.* In Hysterical patients, however, a similar increase, 

 or even a greater one, may take place without any serious cause; thus Dr. 

 Elliotsont mentions a case, in which the respiratory movements of a young 

 female, through nervous affection, were 98 or even 106, whilst the pulse was 

 104. On the other hand, the respirations in certain typhoid conditions and 

 in narcotic poisoning become abnormally slow, owing to the torpid condition of 

 the nervous centres, the proportion being 1 to 6, or even 1 to 8 ; and in such 

 cases, the lungs not unfrequently become cedematous, from the cause formerly 

 mentioned ( 411). 



763. The amount, also, of the Respiratory Movements is affected by vari- 

 ous morbid conditions ; thus when dislocation of the spine takes place above 

 the origin of the intercostal nerves, but below that of the phrenic, so that the 

 former are paralyzed, the respiratory movement is confined to the diaphragm ; 

 and as this is insufficient, serum is effused into the lungs, and a slow Asphyxia 

 supervenes, which usually proves fatal in from three to seven days. Even 

 where the muscles and nerves are all capable of action, the full performance 

 of the inspiratory movements is prevented, by the solidification or engorge- 

 ment of any part of the lung, which interferes with its free distension; or by 

 adhesions between the pleural surfaces, which offer a still more direct impedi- 

 ment. When these adhesions are of long standing, they are commonly stretched 

 into bands, by the continual tension to which they are subjected. If the 

 impeding cause affect both sides, the movements of both will be alike inter- 

 fered with; but if one side only is affected, its movements will be diminished, 

 whilst those of the other remain natural ; and the physician hence frequently 

 derives an indication of great value, in regard to the degree in which the lung 

 is incapable of performing its functions. It is to be remembered, however, 

 that the action both of the diaphragm and of the elevators of the ribs may be 

 prevented, by pain either in the muscles themselves or in the parts which they 

 move ; thus the descent of the diaphragm is checked by inflammation of the 

 abdominal viscera or of the peritoneum ; and that of the intercostals by rheu- 

 matism, pleuritis, pericarditis, or other painful disorders of the parts forming 

 the parietes of the thorax ( 431). 



764. The capacity of the Lungs for air varies considerably in different in- 

 dividuals ; and as the most complete expiration does not by any means empty 



* See a Paper by Dr. Hooker, on the Relation between the Respiratory and Circulating 

 Functions, in the Boston (N. E.) Medical and Surgical Journal ; an abstract of which will be 

 found in British and Foreign Medical Review, vol. vi. p. 263. 



f Physiology, p. 215. note. 



49* 



