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THE CIRCULATION OF THE BLOOD 



suction pressure existed. This conclusion seemed to be confirmed by 

 using a mercury manometer furnished with a valve so arranged that 

 only suction pressure could cause a movement of the mercury (a minimum 

 manometer). The more recent methods, in which optical manometers are 

 used, do not indicate the presence of such a suction pressure and there 

 can be no doubt that the results of the earlier methods were erroneous : 

 those by the spring manometers because of elastic recoil, and those of 

 the minimum manometer because of the inertia of the mercury, the 

 valve catching it, as it were, on the rebound. 



Fig. 35. Diagram to illustrate optical method for recording pressure curves from auricles. 

 A, Auricles; C, Ventricles: B, Aorta; D, Photographic surface. (From Wiggers.) 



Fig. 35 is a diagram taken from Wiggers to demonstrate the optical 

 method of recording simultaneously the pressure changes occurring 

 within the auricle and ventricle and in the aorta. A, B, and C are small 

 chambers filled with fluid and covered with rubber membranes. They 

 are inserted through the walls of the auricle and ventricle and aorta. 

 Each membrane responds to any change in pressure by a minute move- 

 ment which is magnified by reflecting a narrow beam of light from a 

 mirror fastened to its surface. The light beams are focussed upon a 

 moving photographic film. The volume changes are recorded by slip- 

 ping the ventricles as far as their A-V junctions into a glass oncometer 



