RESPIRATION 



The number of respirations in a healthy adult person usually ranges 

 from 14 to 1 8 per minute. It is greater in infancy and childhood. It varies 

 also much according to different circumstances, such as exercise or rest, 

 health or disease, etc. Variations in the number of respirations correspond 

 ordinarily with similar variations in the pulsations of the heart. In health 

 the proportion is about i to 4, or i to 5 ; and when the rapidity of the heart's 

 action is increased, that of the chest movement is commonly increased also, 

 but not in every case in equal proportion. It happens occasionally in disease, 

 especially of the lungs or air-passages, that the number of respiratory acts 

 increases in quicker proportion than the beats of the pulse; and, in other 

 affections, much more commonly, that the number of the pulses is greater 

 in proportion than that of the respirations. 



The Force of Inspiratory and Expiratory Muscles. The force 

 which the inspiratory muscles are capable of exerting on the chest is greatest 

 in individuals of the height of from five feet seven inches to five feet eight 

 inches, and is equal to a column of three inches of mercury. Above this 

 height the force decreases as the stature increases; so that the average 

 power of men of six feet is measured by about two and a half inches of mer- 

 cury. The force manifested in the strongest expiratory acts is, on the 

 average, one-third greater than that exercised in inspiration. But this 

 difference is in a great measure due to the power exerted by the elastic 

 reaction of the walls of the chest; and it is also much influenced by the 

 disproportionate strength which the expiratory muscles attain from their 

 being called into use for other purposes than that of simple expiration. 

 The force of the inspiratory act is, therefore, better adapted than that of 

 the expiratory for testing the muscular strength of the body (John 

 Hutchinson). 



It has been shown that within the limits of ordinary tranquil respiration 

 the elastic resilience of the walls of the chest favors inspiration; and that it 

 is only in deep inspiration that the ribs and rib-cartilages offer an opposing 

 force to their dilatation. In other words, the elastic resilience of the lungs, 

 at the end of an act of ordinary exhalation has drawn the chest walls within 

 the limits of their normal degree of expansion. Under all circumstances, of 

 course, the elastic tissue of the lungs opposes inspiration and favors expiration. 



It is possible that the contractile power which the bronchial tubes and 

 air-vesicles possess, by means of their muscular fibers may assist in expiration. 

 But it is more likely that its chief purpose is to regulate and adapt, in some 

 measure, the quantity of air admitted to the lungs, and to each part of them, 

 according to the supply of blood. The muscular tissue contracts upon and 

 gradually expels collections of mucus, which may have accumulated within 

 the tubes, and which cannot be ejected by forced expiratory efforts, owing 

 to collapse or other morbid conditions of the portion of lung connected with 

 the obstructed tubes (Gairdner). Apart from any of the before-mentioned 



