532 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



of the ribs are especially to be studied, the stethograph may be employed ; 

 if the movements of the diaphragm, a long probe may be inserted 

 through the abdominal walls so that one end rests between the liver and the 

 diaphragm and the other end connects with a recording lever, the abdominal 

 walls serving as a fulcrum. A tracing obtained by one of the above methods 

 shows : (1) That inspiration passes into expiration without an appreciable in- 

 tervening pause ; (2) that inspiration is shorter than expiration ; (3) that the 

 curves of inspiration and expiration differ in certain characters. The relative 

 periods of inspiration and expiration vary with age, sex, and other conditions. 

 The inspiratory phase is shorter relatively in women than in men, and in chil- 

 dren and the aged than in those of middle life. The length of inspiration as 

 compared to expiration is subject to variations, but these relations are affected 

 chiefly by disease and by other abnormal conditions. After section of the 

 pneumogastric nerves, and in diseased conditions which narrow any part of the 

 air-passages, inspiration is longer than expiration, while in emphysema the 

 expiratory phase is prolonged. The relative periods occupied by inspiration 

 and by expiration in the adult differ according to various observers ; at one 

 extreme, the ratio according to Vierordt and Ludwig is 10 : 19-20, and at 

 the other extreme, according to Ewald, 11:12. A mean ratio is 5:6. 

 Rennebaum found that the expiratory phase is relatively prolonged by an 

 increase in the respiration-rate, the ratio being 9 : 10 at 13 respirations per 

 minute, and 9 : 13 at 46 per minute. In the new-born the ratio is 1 : 2-3. 

 Mosso found that during sleep the inspiratory phase is lengthened one-fourth. 



Inspiration is more abrupt than expiration, the lever moving more rapidly 

 during inspiration than during expiration ; consequently the curves differ in 

 character. We may volitionally affect the rhythm and the various phases of 

 each respiratory act. 



A pause may exist between expiration and inspiration (expiratory pause) 

 when the respirations are abnormally infrequent. In certain diseases an inter- 

 val may be observed between inspiration and expiration (inspiratory pause). 

 Some observers look upon the nearly horizontal part of the respiratory curve 

 as a record of a pause, but an examination of tracings of normal respirations 

 shows that one phase passes into the other without an appreciable interval. 



The respiratory acts while we are awake and quiet are rhythmical, but this 

 rhythm is more or less disturbed during sleep, especially in young children 

 and in the aged. In the latter there may not only be an irregularity in 

 the time-intervals between successive acts, but occasionally long expiratory 

 pauses, giving the movements a peculiar periodical character. In the so-called 

 " Cheyne-Stokes respiration " the rhythm is greatly disturbed. This type is 

 characterized by groups of respiratory movements, each group being separated 

 from the preceding and succeeding ones by more or less marked pauses. The 

 first respiration in each group is very shallow and is followed by movements 

 which successively become deeper and deeper until a maximum is reached; 

 then the successive movements become more and more shallow and finally 

 cease. Each group commonly consists of about 10 to 30 respirations, and is 



