284 SWALE VINCENT AND A. T. CAMERON 



consult the original papers of these authors, and from the refer- 

 ences we cannot be certain how far they have dealt with the 

 precise points with which we are most concerned. 



A. THE FROG 



The normal respiration of the frog has been fairly completely 

 studied. A summary of the known facts is given by Baglioni. 3 

 It is sufficient to remark here that a large share in the function 

 of respiration is borne by the skin, the lungs providing an acces- 

 sory mechanism consisting of two separate movements, a) that 

 of the mouth with the lungs closed off and, b) the true lung 

 movements, the latter only occurring at certain intervals. The 

 movements with which we are concerned in this paper are those 

 occurring in the throat and nostrils. (For an account of the 

 normal respiration compare also Willem. 16 ) 



Two different kinds of external influences have been described 

 as affecting the movements in question. Graham Brown, 6 who 

 gives a good account of the literature, deals chiefly with the 

 influence of the nervous system and the labyrinth, but mentions 

 certain external factors producing inhibition, such as shaking of 

 the animal, a blow on the nose, stimulation of the skin, etc. 

 He does not mention the effect of immersion in water or of plug- 

 ging the nostrils. Axenfeld, 1 who seems to have been the first to 

 describe specifically the immersion apnoea in the frog, attributes 

 the phenomenon to a definite stimulation of the nerve endings 

 of the nasal mucous membrane by means of water. Some of 

 the earlier observers referred to by Graham Brown describe an 

 apnoeal reflex in the frog due to various afferent impulses arising 

 from different parts of the body surface. 



The immersion apnoea is one which must have been familiar 

 to naturalists for a long time. The moment that a frog becomes 

 completely immersed in water, the respiratory movements cease, 

 and remain in abeyance as long as the animal continues to be 

 immersed. The most elementary observation shows that cessa- 

 tion of breathing occurs at the moment that both nostrils touch 

 the water. Our observations were directed chiefly toward 

 determining the nature of the stimulus which inhibits the respi- 

 ratory movements. 



