APPARATUS AND METHODS USED IN THIS RESEARCH. 



43 



and the cold current of water descends, thus tending to equalize the 

 temperature of the whole system. By judicious use of ice, a reasonably 

 good control of the temperature can be obtained, even in the warmest 

 weather. 



Spirometer or tension equalizer. — Although an absolute temperature 

 control is theoretically possible with this apparatus, thus securing a 

 constancy in the apparent volume of the air in the closed system, it is 

 practically impossible to prevent slight tem- 

 perature fluctuations, and these, together with 

 the unavoidable and uncontrollable fluctu- 

 ations in barometric pressure, demonstrate the 

 necessity for some form of tension equalizer 

 which will insure atmospheric pressure in the 

 chamber. For this purpose a small spirometer 

 (S) is used. The spirometer regularly attached 

 to the "universal" respiration apparatus is 

 provided with sundry devices for graphically 

 tracing the volume of each respiration and 

 indicating the total ventilation of the lungs 

 when employed with adults. When the infant 

 or dog respiration chamber is employed, the 

 spirometer is used solely as a tension equalizer 

 and accordingly, in figure 3, only those parts 

 are shown which are essential to its use under 

 such conditions. 



The upper part of this spirometer consists of 

 a bell, c, constructed of very light copper or 

 aluminium, suspended by a delicate cord, d, 

 over a pulley, e, and counterpoised by a brass 

 rod, g, g, g. This bell dips into a bath of water 

 or oil in the annular space, b, between the two 

 walls of the lower part of the spirometer. The 

 pipe, a, connects directly with the respiration 

 apparatus. By noting the position of the 

 pointer on the millimeter scale at the right, the 

 exact height of the bell can be seen at any 

 moment. There is no particular compensation 

 device used in connection with this spirometer to allow for the variations 

 of the metal displaced as the bell enters or leaves the liquid ; consequently 

 there are, theoretically at least, slight alterations in the tension with 

 the different positions so that it is advantageous to have the bell in 

 nearly the same position at the beginning and end of each experimental 

 period. It is our practice at the beginning of an experiment, after 

 taking an initial reading of the height of the bell, to introduce a volume 

 of oxygen approximately that which it is assumed that the infant will 



Fig. 3. Spirometer. 

 c, bell of spirometer; d, suspension 

 cord ; e, pulley ; g , g, g, counter- 

 poise; b, water or oil bath; a, 

 air-pipe connecting with the 

 respiration apparatus. 



