40 



COMPARISONS OF RESPIRATORY EXCHANGE. 



Device for measuring the total inspiratory ventilation. — The line directly 

 below the respiration curve in figure 14 was made by the device for 

 recording the total inspiratory ventilation, or the so-called " ventilation 

 adder." An aluminum wheel, 1 r (fig. 13), is attached to the support, s, 

 in such a manner that at each movement of the spirometer bell in a 

 downward direction, that is, at each inhalation, the wheel is mechanically 

 moved by the upward motion of the cord, t. A pawl, u, prevents any 

 perceptible backward motion as the cord is drawn down by the counter- 

 poise, I. By means of a platinum wire, against which a projecting 

 point, w, touches, and a signal magnet not shown in the figure, the 

 total number of revolutions of the wheel can be recorded upon the 

 kymograph drum. The fractional revolution is noted from the reading 

 of a series of numbers on the periphery of the wheel. Each revolution 

 of the wheel corresponds to a movement of the bell through 228 mm., 

 and consequently to a volume of about 4,900 c.c. From the total 



Fig. 14. — Specimen graphic record of respiration. 

 Lowest line, time; middle line, revolutions of the wheel, r (fig. 13). Between 1 and 2, 4 and 5, 

 and 6 and 7, no oxygen was admitted; between 2 and 3 oxygen was admitted at approxi- 

 mately the rate that it was used. At A the three-way valve was turned too early and at B 

 too late. 



number of revolutions and the value per revolution, a calculation may 

 be made of the total amount of air inspired during the time the subject 

 is breathing into the apparatus. 2 



Device for registering number of respirations. — The number of respi- 

 rations in an experiment can be counted from the record made by the 

 excursions of the pointer attached to the counterpoise of the spirometer 

 bell. Since the counting requires considerable time, it is planned to do 

 this automatically by an electrical counting device. The contact por- 

 tion of this arrangement, which has already been installed on one of 

 the respiration apparatus, is shown in detail in figure 13. One end of 

 a platinum wire is fastened loosely around the axis of the aluminum 



*An aluminum wheel, devised by Professor W. T. Porter in connection with his work adder and 

 manufactured by the Harvard Apparatus Co., was used for this purpose. 



2 During the period of an inspiration, the influence of the absorption of carbon dioxide on the one 

 hand and the admission of oxygen on the other involve two more or less compensatory corrections 

 when a high degree of extreme accuracy is desired. 



