114 ' The "Fly-catching Reflex" in the Frog 



action. Also, later than the fly-catching reflex, there come on spinal con- 

 vulsions. These may be due to the supposed action on the bulb — an action 

 similar in nature to that of strychnine — spreading to the spinal cord. 



A third circumstance may possibly have some bearing on the ease with 

 which this snap reflex is elicited in a frog poisoned by yohimbine. "A 

 point of general interest in the physiology of the great alimentary nerve 

 centre in the bulb is the high degree to which it employs inhibition. Each 

 subdivision of it is depressible by inhibitory fibres from some afierent nerve 

 trunk, e.g. respiration by fibres in the superior laryngeal, deglutition by 

 fibres in the superior and partly in the inferior laryngeal nerves " (4). I have 

 noticed in the frog, poisoned either by yohimbine or by other substances 

 which paralyse the respiration, that cessation of the normal respiratory 

 movements is followed for a short time by gulping movements which appear 

 to be movements rather of deglutition than of respiration. The swallowing 

 movements are induced especially by slightly disturbing the frog. Is it 

 possible, as a converse of the stimulation of the laryngeal nerves, that 

 paralysis of the respiration removes some normal inhibitory effect, and so 

 allows a more ready elicitation of the movements of deglutition, and also 

 perhaps of the more complicated fly-catching reflex ? 



Whether yohimbine produces this reflex by a paralysing action on the 

 upper part of the central nervous system (as by operation), or by an action 

 on the medulla oblongata facilitating the elicitation of a latent reflex, or 

 by both actions combined, the phenomenon is interesting as illustrating in 

 a particular manner the close resemblance in the effects produced by 

 operative lesion and toxic action on the nervous system of the frog, and 

 on the other hand, as showing the selective action of a toxic agent on the 

 nervous system, since there may occur in yohimbine poisoning a paralysis 

 of the respiratory centre coincident with an exaggerated activity of the 

 closely related centre for the apprehension of food. 



i 



REFEEENCES. 



(1) ScHRADER, Arch. f. d. ges. Physiol., Bonn, 1887, Bd. xh. 



(2) Sherrington, Schiifer's Textbook of Physiology, vol ii., 1900, p. 837. 



(3) GuNN, Arcliives de Pharniacodynamie, 1908. 



(4) Sherrington, loc cit., p. 887. 



