240 COMPARISONS OF RESPIRATORY EXCHANGE. 



time-consuming and results can not be obtained so quickly as with the 

 Benedict method. If the air is collected directly in the gas-analysis 

 apparatus, the results may be obtained more quickly than if collected 

 in a series of samples and analyzed later. In a series of experiments 

 which can be definitely planned beforehand, this is not an objection. 



In general, it can be stated that the Zuntz-Geppert method for the 

 determination of the respiratory exchange in short periods is more 

 difficult and complicated than the other methods used for this purpose. 

 When the utmost precautions are taken to carry out experiments with 

 this method in the way it should be used, the results of the measure- 

 ments of the total gaseous exchange are reliable and comparable to 

 those secured with the other methods considered in this research. The 

 respiratory quotients are uniform and comparable to those obtained 

 with other apparatus with which either nose- or mouth-breathing 

 is employed. 



TISSOT APPARATUS. 



The general principle of the Tissot apparatus is that of an open- 

 circuit apparatus, i. e., the inspired and expired air are separated and 

 the expired air is collected, measured, and anatyzed. From the results 

 obtained, the respiratory exchange is calculated. The valves used in 

 separating the inspired and expired air are very simple and of very light 

 construction. The flap moves easily, offering practically no resistance 

 to the passage of air. The valves need very little attention other than 

 to see that they are dry and clean as there is no membrane to get out 

 of order or to deteriorate. If properly taken care of, they should 

 last indefinitely. 



The valves have one disadvantage, however, in that the glass con- 

 necting the two metal parts is liable to become disconnected, especially 

 if hot water is used for cleansing them; if accidentally dropped, the glass 

 part is of course easily broken. The valves also have to be kept in a 

 certain position in order to work efficiently. With the glass connection 

 the position of the flap may be readily seen and the valves may be 

 easily adjusted in the proper position on the tee-piece which connects 

 them. The valves may be made less fragile by having the connection 

 made of brass instead of glass, so that the whole valve will be of metal. 

 This method of preventing breakage has the disadvantage that one 

 can not see whether the valves are working properly, but if a notch is 

 made in one end to indicate the proper position for use, and if care is 

 taken to adjust the valves with the aid of this indicator, there is no 

 reason why they should not work efficiently. Practically none of the 

 subjects with whom we experimented complained that the valves did 

 not move freely. Sometimes if the flap becomes clogged by the 

 accumulation of material of any kind it will stick a little before open- 

 ing. This can, however, be remedied by a thorough cleansing and 

 polishing. If the valves are kept clean, the closure is perfect and 



