528 JOHN K. MUELIN 



hap. The blower used with this apparatus gives a ventilation of about 35 

 liters of air per minute when rotating at a speed of 270 revolutions p. ni. 

 Experiment with an alcohol flame shows that this rate of ventilation does 

 not produce a draft which would be perceptible by the infant. The fact 

 that the relative humidity does not become unduly low, even without use 

 of the water bottle, is proof that the infant is sojourning in an atmos- 

 phere approximately normal. 



To remove the moisture coming from the lung and skin of the infant, 

 and any additional moisture from water bottle K, one large-sized Williams 

 bottle B is usually sufficient. However, a second bottle C removes the last 

 traces of water vapor. To facilitate the handling of these bottles in weigh- 

 ing and to prevent breakage, they are usually enclosed in a small wire 

 basket with a handle by means of which they may be suspended directly 

 from a hook on the arm of the balance. 



The Williams bottles as well as the soda lime bottles are fitted with short 

 lengths of rubber tubing of good quality to which are attached respectively 

 male and female parts of ordinary garden hose couplings of standard % 

 inch size ; with a standard rubber hose gasket, the couplings are made air- 

 tight by a single twist of the hand. 



For infants weighing not less than 3 to 5 kgm. the soda lime container 

 holding in the neighborhood of 2 kgm. soda lime is capable of absorbing 

 all the carbon dioxid. This amount of soda lime will take up as much as 

 To gm. C0 2 without renewal. 



The direct determination of oxygen may be made either by weighing 

 the small cylinders of gas L, and noting its loss in weight during the ex- 

 periment, or by passing the gas, under reduced pressure, through a delicate 

 and accurate gas meter. With oxygen made from liquid air a corrective 

 for argon has usually to be made amounting to about 1 per cent. The vol- 

 ume of air inside the respiration chamber is about 75 liters. Correction 

 for temperature change is therefore necessary in order to determine the 

 actual volume of air at the end of every experimental period. Two care- 

 fully calibrated mercury thermometers, one in the cover of the chamber, 

 the other the dry bulb thermometer of the psychrometer, are used to record 

 such changes. While the two thermometers barely read alike, their fluctu- 

 ations are usually parallel. The average of the readings of the two is taken 

 as representing the average temperature of the air in the chamber. 



It is important that the respiration chamber shall not be subjected to 

 sudden fluctuations of temperature during the experimental periods. The 

 water-jacket serves to damp any changes in the room temperature, and by 

 supplying either heat or cold to maintain the chamber at a temperature 

 either above or below that of the room. During cold weather a mercury 

 thermo-regulator placed in the water and connected with a small burner 

 placed underneath, secures a constant temperature which may be regulated 



