286 SWALE VINCENT AND A. T. CAMERON 



nasal apertures, immediately stops the movements of the floor 

 of the mouth. The inhibition is temporary, and lasts from eight 

 to fifteen seconds. Mechanical stimulation of the interior of the 

 nostril does not produce this effect, nor does mechanical stimu- 

 lation of the skin in the neighborhood of the nostril. A weak 

 electrical stimulation in the same neighborhood produces no 

 effect, but a strong stimulation with induced current causes the 

 animal to throw back its head, and this type of action, as ob- 

 served by Graham Brown and others, checks the respiratory 

 movements. But it is interesting to note that when the head is 

 thrown back or pushed back by the hand, in either case there 

 occurs closure of the nostrils concurrently with cessation of 

 respiration, and stimulation of the skin of the back will induce 

 throwing back of the head, closing of the external nares, and 

 stoppage of respiration. 



These changes in some ways simulate the posture reflex ob- 

 served in the duck by Huxley (see below). It should therefore 

 be pointed out here that when a frog is immersed in water or 

 when the nostrils are plugged, no such change of posture need 

 necessarily occur, and does not usually so occur, so that the 

 reflex is not due to this cause. 



4. The following experiment was carried out with two frogs: 

 Fine, accurately fitting cannulae were inserted into the nostrils 

 after cauterizing. The animal was then immersed with the 

 extremities of the cannulae communicating with air; so long as 

 the cannulae were not plugged by mucus, and did not by pres- 

 sure mechanically occlude the nasal passages (these errors were 

 specifically guarded against in the cases observed), respiration 

 went on normally, and no inhibition could be induced such as 

 those described as similar to the postural reflex (it being no 

 longer possible to close the nares). On removing such tubes 

 from the nostrils while the frog was under water, breathing 

 stopped immediately. 



Repetition of this experiment with a number of other frogs 

 gave less satisfactory results, owing to the difficulty of keeping 

 the cannulae free from mucus, etc. In some cases where the 

 cautery had enlarged the aperture of the nostril considerably so 



