INHIBITORY RESPIRATORY REFLEX IN FROG 285 



Axenfeld comes to the conclusion that the nasal mucous 

 membrane is stimulated specifically by air and by water, and 

 that the stimulation calls forth in one case movements of breath- 

 ing, and in the other inhibition of these. He states that 20 

 per cent acetic acid destroys the reflex by damaging the mucous 

 membrane of the nostril; if a frog is immersed after such treat- 

 ment it continues to breathe, filling its mouth with water. 



He also states that the inhibitory reflex is not altered after 

 section of the first division of the fifth nerve with its nasal branch. 



We have carried out the following series of experiments: 



1. Several frogs were treated with 20 per cent acetic acid, 

 following Axenfeld 's directions, and using his precaution of 

 plugging the mouth with absorbent cotton while the nostrils 

 were being treated with the acid, in order to prevent more exten- 

 sive damage. We found that the proceeding interferes with the 

 normal respiration. The animal can no longer breathe properly, 

 even in air. When such an animal is placed in water it is true 

 that it continues the movements of respiration, but this is ren- 

 dered possible by the opening of the mouth to some extent and 

 not through true nasal breathing. The interference with breath- 

 ing in the air is probably due to swelling of the epithelium and 

 excess of mucus in the nasal cavity, and in this case also the 

 animal breathes through the mouth. 



We have repeatedly observed that during free-air breathing 

 when through any cause the nasal passages become obstructed, 

 after a while the animal will continue breathing by occasionally 

 opening and closing the mouth. 



2. More complete destruction of the epithelium of the nasal 

 passage can be produced by the actual cautery. We have done 

 this with several frogs, and if the passage of the nose be kept 

 free something approaching a regular respiration will go on for 

 some time. This, however, ceases instantly on immersing the 

 animal in water. It has been pointed out to us that the cautery 

 will not destroy the epithelium of the deep recesses of the nasal 

 cavity. 



3. Early in our experiments it was noticed that plugging the 

 nostrils with blunt seekers or by placing the fingers over the 



