Iterative excitability in Lillie's nerve model.

Considering the excitability in general as a function of time, Lapicque distinguished the following two cases (1): A. Dans le cas d l'excitation directe, la sommation, ou l'addition latente, d'epends essentiellemnt de la duree des stimuli, tandis que: B. Dans lexcitation indirecte, certaines systemes ou appareils physiologique, peu ou moins sensibles a un stimulus isole, quelle que soit la duree de celui-ci, reagissent dans une large mesure a la reiteration plus ou mains rapide, plus ou mains prolongee de ce stimulus long ou bref. These systems or apparatuses are those which he calls "iterative." The so-called iterative nerve makes a subcategory and contains several nerves intervening between the site of stimulus and the effectors. Whether it is appropriate or not to classify a certain group of nerves as "iterative" has been questioned (2) , but it is not a matter of direct concern in our present problem. We intend, putting this problem aside for the moment, to describe some phenomena observed in modified Lillie's nerve models, in which the stimulus became first effective in producing a certain final event when it was repeated a few times at regular intervals.