NORMAL PROCESSES OF ENERGY METABOLISM 533 



nection with respiration experiments. A form of mask described by Bohr 

 consists of a funnel-shaped piece of tin plate coated on the edges with 

 a substance used by dentists, known on the market as Stent's compound. 

 This substance softens at a temperature a little above the body temperature 

 and may, therefore, be molded to fit the face of each subject. The mask 

 can be made perfectly air tight by covering the molded surface with vase- 

 line or lanolin and binding it securely to the face (Krogh(c)). 



The half mask employed by Boothby is made of rubber on a flexible 

 wire frame so that it may be bent to conform to the shape of the nose, cheeks 

 and chin. It is bordered by a pneumatic cushion. Boothby finds' that it 

 is much safer not to inflate this cushion for the air-valve tends to leak thus 

 altering the pressure against the face and causing leakage. He recom- 

 mends the use of tapes fastened to a towel 

 which lies upon the pillow under the neck of 

 the subject. The tapes may be drawn for- 

 ward and tied about the mask transversely 

 and obliquely in such a way as to apply the 

 pressure just where it is most needed. 

 (Boothby and Sandiford.) (Fig. 12.) 



Hendry, Carpenter and Emmes have shown 

 that the oxygen consumption is practically 

 identical with the different types of breathing 

 appliances adapted to the subject. 



b. Valves. Universally the separation of 

 inspired air from expired air is accomplished 

 by some type of valve. One of the simplest 

 is the well known fluid vah T e of Miiller de- 

 scribed in 1859 (Tigerstedt(/)). Formerly 

 they were much used filled either with water 

 or mercury; but they offer considerable 



resistance to the air and have now been very generally displaced by 

 valves of lighter construction. One form which has been widely used 

 is the valve of Loven consisting of two round brass boxes each enclos- 

 ing a thin membrane of gold-beater's skin or condom rubber (Fig. 13). 

 Small circular apertures suitably spaced and arranged in a circle round 

 the peripheral attachment of the membrane serve for passage of air. The 

 mechanics of this valve will be evident from the figure. Another favorite 

 form is the metal valve of Thiry used by Tissot (Fig. 14). Boothby 

 prefers the so-called flutter valve used in the most recent form of British 

 and American army gas masks. He has devised a metal housing for the 

 rubber flutter and finds the valve in this form perfectly competent. In 

 case of doubt regarding the competency of a valve Boothby recommends 

 the use of two valves one after the other in the inlet or outlet tubing 

 (Boothby and Sandiford). 



Fig. 11. Pneumatic nose- 

 piece of Benedict, a, glass 

 tube to which is fastened a 

 rubber finger-cot, 6, which is 

 drawn over a rubber stopper, 



c. A capillary rubber tube, 



d, serves for dilating the cot 

 6 ; the clamp e closes d after 

 b is inflated. 



