FEEQUENCY AND CHARACTER OF RESPIRATORY MOVEMENTS 479 



the abdominal muscles in expiration gives rise to much higher values. 

 This is also true of those expiratory blasts of air which are made use 

 of in speaking, singing, coughing, and sneezing. Inasmuch as the peri- 

 toneal cavity contains no air, the individual organs are packed closely 

 together. By closing the glottis and simultaneously contracting the 

 diaphragm and abdominal muscles, they may be subjected to a con- 

 siderable pressure, which greatly aids in the expulsion of the feces and 

 urine. This action, which is commonly 

 designated as the "abdominal press," also 

 constitutes an important factor in child- 

 birth. 



Quantitative Determination of the 

 Respired Air. The volume of air which 

 is taken into our lungs during a given 

 period of time, varies with the respiratory 

 needs of our body. Obviously, a much 

 greater quantity of air is required when 

 the tissues are active than when they are 

 inactive. But while the extent and fre- 

 quency of the respiratory movements 

 may serve at any time as an indication 

 of the intensity of the gas interchange, a 

 direct volumetric determination of the 

 air respired is only possible by calibration. 

 The instrument used for this purpose is 

 known as the spirometer. The one de- 

 vised by Hutchinson 1 is a modified gaso- 

 meter (Fig. 248). It consists of a cylin- 

 drical receptacle (B) filled with water, in 

 which is suspended a second cylinder (A) 

 containing air. The latter is counter- 

 balanced by weights (G) in such a manner 

 that it may be made to move with the 

 least possible resistance. The tube (C) 

 enters through the outside cylinder, and is 

 continued upward to a level above the 

 surface of the water in the inside com- 

 partment. If air is expired through this 

 tube, the inside cylinder rises a certain distance out of the water, 

 while if air is inspired through it, the cylinder sinks to a lower level. 

 The amounts of air added or subtracted in this way are indicated 

 by a pointer upon a neighboring centimeter scale. 



In order to be able to determine the volume of the air breathed in 



the course of a long period of time, it is necessary to know two factors, 



namely, the average frequency of the respiratory movements and the 



average volume of air respired each time. It is also possible to solve 



1 Med.-chirurg. transact., xxix, 1846, 137. 



FIG. 248. WINTHICH'S MODI- 

 FICATION OF HUTCHINSON'S SPIRO- 

 METER. (Reichert.) 



