RESPIRATORY MOVEMENTS AND PAUSE. 813 



condition, the walls of the thorax are rendered tense and firm, so as 

 to form a solid base of support for the forcible use of the upper limbs. 

 So also in voluntary or involuntary abdominal expulsive efforts, the 

 chest is usually first filled by an inspiratory act, in which the dia- 

 phragm descends, and then, the glottis being closed, the diaphragm is 

 fixed, and the abdominal and auxiliary expiratory muscles come into 

 action, so as to compress the abdominal contents. 



The movements of inspiration and expiration which constitute a 

 complete respiratory act, succeed each other alternately, from the mo- 

 ment of birth until that of death ; and this character of succession is 

 named the rhythm of the respiratory acts. 



The number of complete respirations in a given time varies accord- 

 ing to many conditions. In the adult, the respirations vary from 14 

 to 18 per minute ; in childhood, at about five years of age, they are 

 said to be about 26 per minute ; whilst at birth, they are as many as 

 40 to 50 ; in extreme age, the frequency of the respirations is again 

 increased. Persons of small stature breathe more quickly, but less 

 deeply than taller people. The respirations are less frequent, but 

 deeper in the male than in the female. The number of respirations 

 is increased by exercise and work, by food, stimulants, and moderate 

 cold, and at great altitudes ; whilst it is diminished in sleep, by mod- 

 erate heat, by increased barometric pressure (see p. 656), by starva- 

 tion, and by depressing influences and agents generally. It is curious 

 that if the attention be directed to the breathing, the number of res- 

 piratory acts is usually diminished. In quick walking, the respirations 

 may be 30 in a minute ; in running, 70 ; and in violent efforts, as 

 many as 100 per minute. In sleep, the respirations are slow, because 

 the interval between expiration and inspiration is unusually prolonged. 

 As elsewhere noticed, there is a-certain ratio, in health, between the 

 number of the respirations and that of the beats of the heart, the 

 proportion between them being in the adult, usually about 1 to 4. In 

 childhood, the respirations are relatively quicker, their proportion to 

 the pulse being from 1 to 3 or 3J. The ordinary ratio between the 

 respirations and the pulse is maintained in the daily and seasonal va- 

 riations of the latter. But in certain diseases it is seriously disturbed, 

 and forms an important guide in medical practice ; thus in pneumonia 

 or inflammation of the lungs, the respirations are so quickened, 

 through embarrassed function, from congestion of the vessels, that 

 the ratio may even be as 1 to 2. In hysteria, the respirations are also 

 much increased in proportion to the pulse. In typhoid states, and in 

 narcotic poisoning, the respirations become so slow, owing to some in- 

 fluence on the nervous centres, that their ratio to the pulse may be as 

 1 to 8. 



The whole period occupied by a complete respiration, is divisible 

 into three stages viz., an inspiratory and an expiratory stage, fol- 

 lowed by a pause, or stage of rest. According to some, there is also 

 a pause between inspiration and expiration, but this can very seldom 

 be recognized or measured. The total period of a respiration, being 

 represented by 10, the inspiratory movement occupies 5 parts, the 

 expiratory 4, and the recognizable pause between this and the succeed- 



