TECHNIQUE FOR METABOLISM DURING REST. 99 



As may be seen, the respiration chamber has relatively few new fea- 

 tures. Indeed, any type of air-tight chamber providing entrance may 

 be employed, but this particular type of construction seemed to us best 

 suited for the special purpose of the Nutrition Laboratory. ^ As will be 

 shown later, the shape and size of the chamber play a relatively small 

 role. The entrance may be changed to one end of the chamber, if 

 desired; and for experiments with large wild or domestic animate, such 

 a change in location would be practically necessary. Heat may be 

 brought away without using a brine coil if the chamber is perfectly air- 

 tight and some adequate system of cooling is used, such as exposing the 

 metal walls to the free circulation of indoor air, rather than, as here 

 shown, protecting them by sheathing, dead-air space, and finally compo 

 board. The essentially novel feature of the whole installation is the 

 maintenance, aliquoting, and analyzing of the ventilating air-circuit. 



VENTILATION OF RESPIRATION CHAMBER. 



As may be noted in figure 6, air is taken from outdoors and delivered 

 by means of a rotary air-impeller, k, through an opening, h, near the 

 top of the chamber. Since on many days in winter the outdoor air is 

 extremely cold, it has been necessary at times to warm the air. This is 

 done by means of a Bunsen burner, m, with a small hood, attached to 

 the outside of the sheet metal pipe carrying the air from the blower to 

 the chamber. By regulating the size of this flame, any degree of tem- 

 perature may be secured for the air entering the chamber. Butterfly 

 valves, n, in the air-pipe control the amount of air delivered to the 

 chamber and may be adjusted at will, irrespective of the speed of the 

 blower. For practically all experiments thus far made we have used 

 only a fraction of the possible discharge from the blower and the cross 

 section of the pipe has always been considerably reduced by turning 

 the butterfly valve. 



INCOMING AIR. 



The incoming air is taken from a point outside the north window of 

 the building. The pipe on the intake side of the blower enters the 

 calorimeter laboratory through a board fitted into one of the windows 

 and has a diameter of 6 inches. The pipe between the blower and the 

 chamber has a somewhat smaller diameter, 4 inches. No provision is 

 made for noting directly the amount of air entering the chamber or its 

 degree of humidity. In fact, as will be seen later, no analysis is made 

 of the ingoing air. This is one of the simplified features of the appa- 

 ratus. Care is taken to deliver to the chamber only uncontaminated 

 outside air. Repeated analyses of air in the neighborhood of the 

 Nutrition Laboratory have shown that, for all practical purposes, the 

 carbon-dioxide content is constant, irrespective of weather conditions, 

 temperature, or season.^ 



1 Benedict, Carnegie Inst. Wash. Pub. No. 166, 1912, p. 114. 



