RESPIRA T1ON. 121 



given it by the spiral spring. In every case the elas- 

 ticity of the elastic band must be less than that of the 

 spiral spring, otherwise the rubber button would not 

 follow the movements of the thoracic wall. So adjust 

 the apparatus that every movement, however slight, 

 of the button will be instantly responded to by the 

 lever. 

 .'} Observations. 



(9) Carefully measure the arms of the lever to deter- 

 mine how much the tracing point of the lever will 

 move for every millimeter that the button moves. 



(10) When the button is pressed outward in inspira- 

 tion what direction does the lever move? 



(11) Take tracings of the changes in the dorso ven- 

 tral diameter at the level of the nipples. Deter- 

 mine by measuring the tracing how much the 

 dorso ventral expansion is. What is the average 

 expansion during normal, quiet breathing ? What 

 is the expansion during forced respiration ? 



(12) Make a similar series of observations on the 

 lateral diameter in the plane of the nipples. 



(13) Repeat observations on the lateral ninth rib 

 diameter. 



c. The belt=spirograph. Substitute for the rod of the 

 thoracometer which bears the button and spring, a 

 plain wooden or iron rod. Place the belt-spirograph 

 around the subject at any level of the body, whose 

 varying girth is to be observed. The fish cord used 

 in the previous experiment may be transferred to this 

 instrument. Tie one end into the eye in pulley No. 1, 

 pass it over the other pulleys and to the lever; the 

 horizontal bars may be, raised to the axillae and will 

 serve to steady the subject. The expansion in girth of 

 thorax is so great that it may be found necessary to 



