XII 



MECHANICS OF KESPIEATION 



415 



found in dogs, cats, and rabbits that with forced respiration 

 the intercartilaginous muscles contract synchronously with the 

 diaphragm, i.e. are inspiratory, which was confirmed later on by 

 Bergendall and Bergmann. B. Fick 

 (1897) made an exhaustive in- 

 vestigation of the subject, both 

 critically and by means of vivi- 

 sections on dogs, and came to the 

 same conclusion. 



Besides the internal interos- 

 seous intercostals, all the muscles 

 contained in the depth of the ab- 

 dominal wall act as inspiratory by 

 compressing the abdominal viscera, 

 thus pushing the diaphragm up- 

 wards and the lower ribs down- 

 wards. Such are the rectal 

 abdominal, the oblique external 

 and internal, and also the trans- 

 verse muscles. 



The instruments used in measuring 

 the different diameters of the thorax, 

 and the variations which these undergo 

 during normal and forced respiration, 

 are known as thoracometers. That of 

 Sibson, represented in Fig. 181, is the 

 most generally used, and is easy to 



apply 



FIG. 181. Sibson's Thoracoineter. Two 

 metal rods at a right angle, D is applied 

 to vertebral column, and B (which runs 

 along the graduated scale C) carries at 

 its extremity a toothed rod A, provided 

 with a button to be applied to the 

 sternum. This moves an index, which 

 shows the excursions, magnified on a 

 dial. 



[f this instrument is reduced to the form of a measuring compass 

 (callipers), the limb A, which runs in a cogged wheel, and moves the 

 indicator of the dial, being replaced by a capsule covered with a rubber 

 membrane, kept taut by an elastic spring, and provided with a button, the 



FIG. 182. Marey's Pneumograph (latest model). Flexible steel plate, curved by the traction of 

 two arms of a lever joined at the circumference of the thorax by a silk band. The curve of the 

 plate is shown by a lever attached to the centre of the elastic membrane of an exploring 

 tambour. This records the pneumogram inversely upon a revolving drum, i.e. the descending 

 line corresponds with the inspiratory dilatation of the thorax, and the ascending line with 

 its expiratory retraction. 



respiratory variations of any given thoracic diameter can be registered on a 

 revolving cylinder. 



This is the model on which the thoracograph of Bert and of Fick, and 

 the stethograph of Burdoii-Sanderson are constructed. 



Marey's pneumograph (Fig. 182), of which there are various types, makes 



