KESPIRATION OF DYTISCUS MARGINALIS L. 345 



Exyeriment B. Animal in the water during If hours. Before 

 the experiment: 10.18 cc. thiosulphate. Afterwards: 9.82 cc. 

 Difference: 0.36 cc. thiosulphate. 



Unfortunately, I cannot find the volume of the water used in 

 these experiments in my records. Nevertheless, their results 

 prove that some oxygen has disappeared from the water, and 

 this is the only point I wished to state. 



5. A glance at the figures given in table 1 for the composition 

 of the air in the animal's store immediately after diving shows 

 us that this air contains an abnormally high percentage of carbon 

 dioxide. The figures of Ege and of Kreuger agree in this respect 

 completely with my own. We may therefore safely conclude 

 that this air is a mixture of expired and atmospheric air, a 

 'Mischungsluft.' 



My first impression of the fact that the first phase of the 

 breathing process is not an 'inspiratorische Schluckbewegung,' 

 but an expiration, was that it would compHcate our present 

 knowledge of the problem to such an extent as to make it a 

 chaos of contradicting facts. Certainly, it proves that a great 

 deal of the literature based on this hypothesis is worthless. 



It is clear that the only way in which the animal can cause a 

 movement of the droplet in the direction of the distal end of the 

 tube is by reducing the pressure somewhere else, and it is very 

 probable that this reduced pressure will be in its tracheal system 

 and tissues. As the animal's body fluids are incompressible, no 

 other possibility can be realized. 



Let us now suppose that in diving the animal takes with it a 

 certain quantity of air, A. The oxygen in the air-store is used 

 up as I showed in 1 . The animal gives off carbon dioxide instead 

 of this oxygen, but, as the analyses of three authors show, this 

 CO2 diffuses out very soon into the water. Consequently the 

 volume of the air-store must diminish. Moreover, after some 

 time, as both CO2 and Oo are very low, the partial pressure 

 of nitrogen will be higher than in the water, which is in equilibrium 

 with the air, and nitrogen will diffuse out. All these factors tend 

 to diminish the total volume of the air-store and make it less 



