350 UNIVERSITY OF COLORADO STUDIES 



other.^') It may be that the effect of steady pressure may cause a 

 general diffused hyperaemia, whereas the stimulation resulting in the 

 phenomena of tickling may and undoubtedly does cause a sudden 

 convulsive hyperaemia which entails an explosive motor discharge. 

 This relief of sudden congestion by additional stimulation of other 

 and different nerve endings is observable in the relief afforded by 

 rubbing or stroking a part which has been pinched or bruised, or by 

 scratching an itching spot. 



An additional causal factor in the production of tickling may lie 

 in the nature and structure of the nervous process involved in per- 

 ception in general. According to certain histological researches of 

 recent years (^^ we know that between the sense organs and the central 

 nervous system there exist closely connected chains of conductors or 

 neurons, along which an impression received by a single sensory cell 

 on the periphery is propagated avalanche-like through an increasing 

 number of neurons until the brain is reached. If on the periphery a 

 single cell is excited, the avalanche-like process continues until finally 

 hundreds or thousands of nerve cells in the cortex are aroused to con- 

 siderable activity. Golgi, Ramon y Cajal, Koelliker, Held, Retzius 

 and others have demonstrated the histological basis of this law for 

 vision, hearing and smell, and we may safely assume from the phe- 

 nomena of tickling that the sense of touch is not lacking in a similar 

 arrangement. The importance of this law, it may be incidentally 

 remarked, is manifest at a glance, for a future science of education. 

 The spread of all methods whereby first-hand information is gained, 

 while empirically found to be eminently satisfactory, is now known 

 to rest upon a scientific basis. The laboratory method, kindergarten 

 and primary object lessons, and constructive work, the use of illus- 

 trations in textbooks, magazines and newspapers, the stereopticon, 

 etc., etc., may be cited as empirical recognition of this scientific fact. 



May not a suggestion be offered with some plausibility, that 

 even an ideal or representative tickling, where tickling results, say. 



(1) Lauder Brunton, 'On Inhibition.' 'West Ridiner Asylum Reports,' 1874, p. 179, and Nature, 



1883. Vol. XXVII. 



(2) Ramon y Cajal, 'Einige Hypothesen uber den anatomischen Mechanismus der Ideenbild- 



ung. der Association und der Aufmerksamkeit,' Archiv fur Anatomie und Entwicke- 

 iun(j^fiegchichte, Jahrgang 1895, pp. 367 flf. 



