544: JOHN R. MURLIN 



the volume recorded by a meter is independent of the rate only within 

 certain limits corresponding roughly to 100 complete revolutions per hour 

 ( Krogh (c) ) . As Benedict has shown the volumes recorded at higher rates 

 than this are smaller than the actual volumes, but if the high rate is constant 

 and the meter is calibrated at such a rate it is quite possible to record vol- 

 umes with no appreciable error. In such a method as that of Hanriot and 

 Richet the meter employed for measuring the respiration of a man at rest 

 should be capable of measuring correctly not less than 12 meters per 

 revolution, and since in heavy muscular work the total ventilation may 

 be multiplied tenfold over that of the resting rate of respiration a meter 

 for measuring the ventilation of the lungs would need to have a capacity 

 of 120 meters. Krogh has recently devised a spirometer for calibrating 

 gas meters which should simplify this process and render the use of gas 

 meters much more reliable. In the paper describing this, apparatus Krogh 

 notes that in wet meters with a constant quantity of water the volume 

 per revolution increases with increasing rate but can be determined with 

 sufficient accuracy. Dry gas meters he finds are much less accurate than 

 wet test meters. 



2. Closed Circuit Instruments. There ax0 two well-known forms 

 of respiration apparatus used with mouth-pieces or nose-pieces and con- 

 structed on the closed-circuit principle. The first of these is the so-called 

 Universal respiration apparatus of Benedict (d) (e) ; and the second is a 

 modification of the instrument constructed by Haldane and Douglas de- 

 vised by Krogh (a). To speak of the second form first, Krogh has so de- 

 vised his instrument that it may be used continuously for a considerable 

 period of time by a man at rest. The soda lime absorber is capable of re- 

 taining 1000 liters of carbon dioxid. Oxygen is admitted from a cylinder, 

 being passed through a meter which records electrically by closing a circuit 

 each time the meter revolves once and has, therefore, passed a certain vol- 

 ume of oxygen. A recording spirometer gives a quantitative record of 

 the respiratory movements. Only oxygen absorption is determined as the 

 apparatus is usually employed, but carbon dioxid determinations can be 

 made by drawing samples of inspired and expired air from certain parts 

 of the apparatus. So far as known to the writer this form of apparatus 

 has never been used in the United States. 



The apparatus of Benedict on the other hand has been used quite ex- 

 tensively. The writer has made almost continuous use of one of these 

 over a period of nearly twelve years. It has been modified and improved 

 from time to time and is used to-day as shown in Fig. 21. Attachment 

 to the respiratory passages of the subject is effected by means of the 

 Denayrouse mouth-piece or the rubber nose-pieces of Benedict. Quite re- 

 cently also the half mask of Boothby has been adapted to this use and has 

 given much satisfaction. It is far more comfortable than either the mouth- 

 piece or the nose-piece. The apparatus is constructed with three trains 



