METHODS OF MEASURING RESPIRATORY EXCHANGE 47 



numerous respiration experiments, has been described by Tangl [1903] 

 (fig. 1 9). He uses a three-way tap connected with the trachea and turned 

 at a uniform rate by means of a motor. The inspiration tube of this 

 tap can be connected as in the figure with a pump with one valve driven 

 from the same shaft as the tap, so that it will press a certain volume of 

 air into the lungs each time the tap is opened. An alternative method, 

 which in the opinion of the writer is absolutely preferable, is to connect 



FIG. 19. From Pfliiger's " Archiv ". 



the inspiration tube with a supply of air at a slight constant pressure 

 (usually 8 to 1 2 cm. of water). The expiration tube is connected with 

 a gas meter and sampling arrangement. 



2. Methods for Studying the Respiratory Exchange of Aquatic 



Animals. 



The technique of respiration experiments on aquatic animals must 

 be based on the properties of the respiratory gases when dissolved in 

 water, properties which differ considerably from those shown by the 

 free gases. 



