38 GASEOUS METABOLISM OF INFANTS. 



recently have shown that in a specially constructed and very delicate 

 psychrometer the depression of the wet-bulb thermometer can be 

 measured with great accuracy and the amount of water-vapor in the 

 air computed with an exactness sufficient for all practical purposes. 

 The construction of this psychrometer, Z, is very simple. Two ther- 

 mometers, each graduated in 0.1 degree and capable of being read with 

 a lens to 0.01 degree, are placed in the air-circuit leading from the 

 respiration chamber. The thermometer nearest to the chamber is the 

 dry-bulb thermometer; around the bulb of the other thermometer is 

 lightly attached a piece of fine linen which is continually kept moist 

 with water drawn from a small reservoir by capillary attraction. By 

 the use of the well-known psychrometric tables, it is possible to compute 

 from the depression of the temperature the tension of the water-vapor, 

 the degree of humidity, and the actual amount of moisture in the air. 

 With the large respiration calorimeters, this has been carefully con- 

 trolled both by the aspirator method— that is, by the aspiration of a 

 certain volume of air over pumice-stone — and more particularly by 

 the use of the extraordinarily ingenious and accurate psychrometer 1 of 

 Dr. Klas Sonden of Stockholm. 



The wet- and dry-bulb psychrometer as thus constructed gives most 

 satisfactory results. It is, however, of the highest importance to make 

 sure that the cloth around the wet-bulb thermometer is kept thoroughly 

 drenched with distilled water, also that the capillarity of the fiber is 

 good, as otherwise the cloth may become partially dried and inaccurate 

 results obtained. Prior to each experiment, the wet bulb is drenched 

 by using an elongated medicine dropper rilled with distilled water. 



Muffler.— Since a rotary pump is used to keep the current of air in 

 motion, which rapidly draws in successive small portions of air, a 

 puffing sound is produced which has proved somewhat disturbing to 

 certain infants. To eliminate this, a small muffler, N, consisting of a 

 brass can filled with cotton batting, is placed between the psychrometer 

 and the blower. 



Blower.— After experimenting with many different types of blowers, 

 we have found the most satisfactory to be that furnished by the Crowell 

 Manufacturing Company of Brooklyn, New York, under the specifica- 

 tion No. O-D Rotary Compressor. This can be secured from the 

 manufacturers in a surrounding iron box, which is suitable for an oil- 

 immersion bath. It is a positive blower in that the air withdrawn from 

 the chamber may be forced through a considerable number of layers of 

 sulphuric acid and soda lime contained in suitable vessels. The blower 

 (P) is connected by a leather belt to a small electric motor and can be 

 provided with a safety clutch to prevent the reversing of the wheel 

 through carelessness and the drawing over of sulphuric acid fro m the 



Sonden, Bihang till K. Svenska Vet.-Akad. Handlingar, 1891, 17, p. 3; see also Meteorologisehe 

 Zeitschr., 1892, p. 81. 



