INHIBITORY RESPIRATORY REFLEX IN FROG 287 



that the cannulae did not completely occlude it, immersion of 

 the animal, snout-end last, caused immediate cessation of respi- 

 ratory movements, apparently through the entry of water into 

 the nostrils round the outside of the cannulae. 



In all the above experiments similar effects were produced by 

 immersion in water, whether the animal was immersed snout 

 first or snout last, except in cases where the mucous membrane 

 of the nostrils had been damaged, when change of posture pro- 

 duced an effect in some animals, this being almost certainly due 

 to increased or decreased plugging of the nostrils with mucus. 



5. Cannulae were inserted into the nostrils of an intact animal; 

 the respiratory movements were seriously affected, but after 

 some minutes an imperfect kind of respiration began. The free 

 ends of the cannulae were then immersed in water, and after 

 several seconds the same imperfect respiratory movements 

 recommenced, although only water could be taken in. This 

 occurred even when the nostrils were also submerged. 



All these experiments were carried out with R. pipiens from 

 Illinois. 



Conclusions 



Apparently Axenfeld is right in supposing that the most 

 important factor in the submersion stoppage of respiratory 

 movements is a specific stimulation of the nasal mucous mem- 

 brane by contact with water. This is supported by our experi- 

 ments nos. 4 and 5, and is not definitely contradicted by no. 2. 

 It may be observed in this place that this inhibition of the 

 respiratory movements is more pronounced and permanent in 

 the frog than in other classes of animals, since, as shown by 

 experiments carried out in this laboratory, 7 the animal can live 

 for many weeks under water, and during this time makes no 

 attempt at respiratory movements, the floor of the mouth 

 remaining permanently in the expiratory position. 



In addition to the reflex described above, there appears to be 

 another and quite separate one, caused by plugging the nostrils 

 (cf. experiment 3). We are tempted to suggest that the sense 

 of resistance brought about by the impeded air flow and experi- 



