282 MECHANISM OF THE RESPIRATORY MOVEMENTS. 



pressures amount to from -30 to -74 mm. Hg in inspiration, and to 

 from about -+62 to +100 mm. Hg in expiration (Donders). 



Methods of registering the respiratory movements. — The methods 

 of registration can be divided into four classes — 



1. In the first class the expansion and contraction of the thorax are 

 recorded. To this end Marey devised his pneumograph, which consists of a 

 cylinder with elastic ends, the interior of which is connected with a recording 

 tambour. A strap or cord attached to the membrane, closing the two ends of 

 the cylinder, is passed round the chest. As the thorax expands, the membrane 

 at each end of the cylinder is drawn out. The rarefaction of the air in the 

 cylinder thus produced is transmitted to the tambour and causes a fall of the 

 lever. 



Burdon Sanderson's stethompfer consists of a rigid rectangular framework, 

 formed of two bars joined by a cross piece. The distance between the bars 

 can be adjusted to fit the antero-posterior diameter of the subject under 

 investigation. The free ends of the bars are provided, one with an ivory button 

 which rests on the spine of a vertebra, the other with a tambour, the knob of 

 which presses against the sternum. An increase in the antero-posterior 

 diameter of the chest presses on the button of the tambour, and the move- 

 ment thus produced is transmitted by a rubber tube to another recording 

 tambour. 



2. Another method is to record in animals the movements of the column of 

 air which enters and leaves the kings at each respiration. One method of doing 

 this is to attach a T-piece to the tracheal cannula, one limb of the T being left 

 open, while the other is attached to a large vessel of air, which is also connected 

 with a Marey 's tambour. When it is desired to record the movements the 

 free end of the T-piece is clamped, so that the animal now breathes in and 

 out of the receiver, and the consequent changes of pressure in this vessel are 

 transmitted to the Marey's tambour and recorded. This method surfers 

 from the drawback that the air in the receiver soon becomes vitiated, so that 

 the breathing is altered, and it is necessary to interrupt the observation in 

 order to renew the air. 



Gad l has used a modification of this method in nearly all his researches. 

 This observer's pneumatograph, which is substituted for the Marey's tambour 

 employed in the method just described, is a light open box of mica, which is 

 counterpoised so as to rest face downwards in a vessel of water. To the 

 bottom of the box is attached a lever, the movements of which can be recorded 

 on a blackened surface. The interior of the box is connected with a large 

 air chamber into which the animal breathes. Each inspiration causes a 

 sucking of air out of the box into the air chamber, so that the pneumatograph 

 sinks in the water, whereas each expiration will increase the volume of air, 

 and so cause a rise of the pneumatograph with its lever. 



3. Since each respiratory movement causes a change in the intrathoracic 

 pressure, it is evident that a record of these variations may be used as 

 evidence of the respiratory movements. These variations may be studied by 

 introducing a cannula connected with a manometer or tambour into the 

 pleural cavity, or by introducing an elastic sound connected with a registering 

 tambour through the mouth into the oesophagus. The latter method has been 

 used especially by Rosenthal. 2 



4. Since the diaphragm is in the higher animals the most important 

 inspiratory muscle, and in rabbits is practically the only active muscle in 

 quiet respiration, it is obviously of advantage to record its movements directly. 

 Many methods for recording the contractions of the diaphragm have been 

 devised. 



1 Arch. /'. Physiol., Leipzig, 1879, S. 181. 



- Hermann's "Handbuch," Bd. iv. Th. 2, S. 163-286. 



