556 METABOLISM 



is taken, washed free from salt by allowing water from the tap to run 

 through it, and softened in a weak glycerine solution. The gut becomes 

 very soft and pliable, and does not dry quickly. A piece of the casing 

 about 10 cm. long is threaded through a glass tube of about 15 mm. bore 

 and 4 to 6 cm. long. One end of the casing is brought around the outside 

 of the tubing and secured by means of a thread. The lower end of the 

 membrane is pinched off and the casing is then cut a little more than 

 half way across its middle, so that the opening will lie just within the 

 free end of the tube when the casing is drawn back through it. The 

 loose end of the casing is slightly twisted an essential procedure and 

 is then secured by a thread on the outer side of the tube. If properly 

 made, the valve will work freely without vibration, and the opening be 

 sufficiently large to allow a good current of air to pass. It should col- 

 lapse instantly and be air-tight when the current of air is reversed. The 

 back lash, or lag of closure, of these valves is extremely small, and 

 they will open or close with a pressure of air not exceeding the pressure 



Fig. 178. Diagram of respiratory valves. 



changes in normal respiration. When not in use, the valves should be 

 kept in glycerine water on ice. Valves prepared in this way have been 

 in use a month without loss of efficiency. They are, however, made with 

 so great ease that new valves are provided for each subject, and they are 

 therefore especially adapted to ward work (Fig. 178). 



The valves are inserted in reverse order into a supporting metal 

 T-piece, and the joints made air-tight by tape. The stem of the T is 

 connected with the mouthpiece. Through a rubber tube of about 3/4 

 inch bore, the expired air is collected in the spirometer, or Douglas Bag. 



3. THE TISSOT SPIROMETER is pictured in Fig. 179. We have found the 

 100-liter size to be very serviceable in the clinic. This instrument is 

 mounted on a platform having rubber wheels, and can be moved about 

 the wards with ease. The bell of the spirometer is made of aluminum 

 and is suspended in a water-bath between the double walls of a hollow 

 cylinder made of galvanized iron. The height of the bell is 72 cm. 

 and the diameter 42 cm. An opening at the bottom of the 

 cylinder connects through a three-way stopcock with the rubber tube 

 leading from the expiratory valve of the mouthpiece (see Fig. 177). 



