420 PHYSIOLOGY' CHAP. 



rises during expiration and sinks during inspiration. This fact 

 increases the probability that in man also the normal expiratory 

 movements are active, even if this be due to participation of the 

 internal intercostals, and not of the abdominal muscles. 



The most convincing evidence for the active character of 

 expiration under normal conditions also was, however, furnished 

 by Aducco (1887). From a series of ingenious experiments per- 

 formed on men and dogs, he adduced the following facts, which 

 show as a whole that in the expiratory process the contraction of 

 certain muscles co-operates with the elastic reaction of the lungs, 

 thorax, abdominal walls, and intestinal gases : 



(-) Normal expiration, being favoured by many passive factors, 

 has in the waking state a longer duration than inspiration, which 

 meets with corresponding resistance from these same factors. 



(&) Expiration proceeds quite regularly, even when some of its 

 principal passive factors are excluded, e.y. after the abdominal and 



FIG. 185. Pneumograms taken with Jlarey's pneumograph during normal, quiet breathing. 

 The lower abscissa is at the level of the dead point of the deepest inspirations ; the higher 

 abscissa at the dead point of the more active expirations. 



thoracic cavities have been widely opened to exclude the elastic 

 reaction of the intestinal gases and distended lungs. 



(c) When to the passive factors of expiration is added a force 

 which works in the same direction (a rubber sheath compressing 

 the thorax, a weight placed on the thorax), the time relations 

 between the two acts of respiration is very little altered. 



(d) With artificial expiration on the dead body, when only 

 passive factors can come into play, a given weight is invariably 

 less displaced by the thoracic walls than in normal expiration. 



(e) Given two expirations of equal strength, one made by the 

 living animal, the other artificially induced on a dead body of the 

 same, the positive tracheal pressure developed by the latter is 

 lower. 



(/) If during sleep, thoracic and abdominal pneumograms are 

 taken on a person breathing through Miiller's water-valves, and 

 the pressure raised in the expiratory valve by adding a little water, 

 the curve (Fig. 186) shows that while thoracic expiration undergoes 



