THE BUILDING OF REFLEX ARCS 253 



discontinued at the time of their occurrence, and to be suppressed 

 on subsequent similar occasions." 



In this connection a statement from Professor McDougall's 

 work may be advantageously quoted. He says that " It is charac- 

 teristic of those (arcs) of the higher or third level that their organisa- 

 tion, their interconnections, by means of which the simpler neural 

 systems of great complexity, is congenitally determined in a very 

 partial degree only, and is principally determined in each individual 

 by the course of its experience. The arcs of the higher level thus 

 constitute the physiological basis or condition of docility, the power 

 of learning by experience." 1 (My italics) 



Scratch Reflex of the Cat. 



There is a notable difference between the scratch -reflex of the 

 dog and that of the cat, especially as to the site of its receptive- 

 field. That of the dog has been referred to, but it appears to be 

 generally accepted that the cat has no such saddle-shaped or indeed 

 other area of skin receptive-field on its back or flanks. I have 

 repeatedly tried by various mechanical stimuli, applied both 

 irregularly and rhythmically, to evoke a scratch -reflex in a cat, 

 young or adult, on the surface corresponding to that of the dog, 

 and have found no response. This has been tried both when the 

 animal was awake and when asleep. But the receptive field of the 

 cat's scratch -reflex has received careful and elaborate attention, 

 which is described in a paper by Professor Sherrington in the Journal 

 of Physiology, Vol. LI. No. 6. By means of delicate stimuli, 

 mechanical and electrical in a decebrate cat, the receptive-field 

 of the scratch-reflex has been accurately delineated in the pinna, 

 and several other pure reflexes have been obtained. These are 

 protective of the pinna ; some, the retraction and folding reflexes 

 seem directed against irritant touches, e.g. the settling of fleas — 

 or against exposure to injury in fighting ; others, the cover and 

 head -shake and scratch -reflexes against the ingress of foreign matter, 

 such as dust, water, insects, into the meatus and ampulla. The 

 threshold for their elicitation is extremely low, that is to say, they 

 require very gentle stimuli to evoke them, while with the exception 

 of the scratch -reflex they are elicited with difficulty and uncertainty 

 by electrical stimuli (My italics) to which the animal has been sub- 

 jected in the course of its total experience. He adds that the pinnal 

 reflexes are readily obtained in the normal animal, and I may allude 

 here to some small observations I made on a normal young cat 



1 Op cit. p. 21. 



