460 PHYSIOLOGY CHAP. 



(a) If on a tracheotomised rabbit, with intact vagi, breathing 

 normally, rhythmical insufflations (positive ventilation) or 

 rhythmical aspirations of air (negative ventilation) are made 

 through the tracheal cannula, so that in the first case rhythmical 

 dilatation, and in the second, rhythmical retraction of the lungs, is 

 produced, it will be seen that the animal reacts to each insufflation 

 by an expiration, as plainly shown by the constriction of the nasal 

 pinnae, and to each aspiration of air by an inspiration, as evidenced 

 by the widening of the nostrils. If the insufflations or aspirations 

 are retarded or accelerated, the animal adapts its respiration to the 

 required rhythm by making the opposite movement, i.e. it reacts 

 with an expiration to each dilatation, with an inspiration to each 

 contraction of the lungs. This harmony between natural and 

 artificial respiration ceases absolutely after section of the vagi. - 



(6) If the rubber ring attached to the tracheal cannula of an- 

 animal (with intact vagi and regular respiration) is constricted or 

 occluded at the moment at which expiration ceases and inspiration' 

 sets in, it will be seen that the latter lasts far longer. If, on the 

 contrary, the trachea is constricted or occluded at the close of an 

 inspiration and commencement of an expiration, the animal is 

 seen 'to extend its expirations and remain longer in the expiratory 

 posture. These effects cease after section of the vagus.. 



(c) When a ventilating apparatus is attached to the tracheal 

 cannula of a dog or rabbit, which favours inspiration and hinders 

 expiration, so that the extent of pulmonary distension increases at 

 each inspiratory act, it is seen that the expiratory acts consequent 

 on the successive inspirations become longer and more energetic, 

 until the tetanic force of the expiratory abdominal muscles ejects 

 the ventilating apparatus from the cannula. 



(d) If in an animal with normal respiration, double pneumo- 

 thorax is suddenly produced by opening the two pleural cavities, 

 the vagi being intact, a deep and prolonged inspiration follows a 

 true inspiratory tetanus. 



(e) Similar facts are met with clinically, when in consequence 

 of any kind of morbid condition the expiratory retraction or 

 inspiratory dilatation of the lungs encounters some obstacle. In 

 the first case (e.g. in pulmonary emphysema) expiration, in 

 the second (e.g. stenosis of the larynx or trachea, plural or peri- 

 cardial effusions, etc.) inspiration, is prolonged. 



In the year 1888 Stefani and Sighicelli (in continuation of the 

 researches of Hering and Breuer) endeavoured to determine what 

 changes in respiratory rhythm occurred when a rabbit was made 

 to pass rapidly from breathing air under normal pressure to 

 respiration at higher or lower pressures, so that the lungs became 

 passively dilated or contracted. The method consisted in applying 

 a T-cannula with a three-way tap to the animal's trachea. One 

 of the outer branches of this cannula communicated freely with 



