Zur Physiologie Der Angeborenen Auslösenden Mechanismen

An attempt is made to see into the Physiology of the I.R.M. by the quantitative analysis of the internal and external factors connected with the release and discharge of gaping reactions in Green finches (Chloris chloris L.) ; Chaffinches (Fringilla coeleps L.), Hawfinches (Coccothraustes coccothraustes L.), Linnets (Carduelis cannabina L.). The results are compared with those obtained with Bullfinch (Pyrrhula pyrrhula L.), Nuthatch (Sitta europaea L.), Spotted flycatcher (Murcicapa striata Pallas.) and Swallow (Hirundo rustica L.). Over 4000 actual gaping reactions are involved. 1. In those species of seed eating birds examined the intensity and duration of the discharge of a single gaping reaction is dependent upon the kind and not upon the intensity of the stimulus. The all-or-none-rule must be applied. In insect eating species the duration and intensity of the reaction is dependent upon the strength of the stimulus. 2. If any releasing stimulus is repeated it becomes ineffective when a certain number, constant for the species and state of development, has been given. This property common to all instinctive acts was explained by the exhaustion of the so-called reaction specific energy in the efferent centre. That the sign stimuly become ineffective is due only to an adaptation in the afferent apparatus. This can be shown by successive combinations of different stimuli. 3. In 5-7 day old Chaffinches shaking of the nest and the imitated call of the parents are equally effective - as measured by the number of gaping reactions elicited by stimuli given every 2 seconds. By giving either stimulus until it becomes ineffective one can get 10-13 reactions. If however they are given alternately each a few times only the young gape 40-46 times. It seems that the adaptation is a kind of breaking mechanism preventing a too frequent performance of an instinctive act. 4. In some species sleep occurs in definite periods. Nuthatchers of a few days old will gape only at intervals of five minutes. In other species the clear cut rhythm is absent but even in them sleep shows all the properties of an activity. It seems clear that sleep inhibits the performance of a gaping reaction. 5. When nestlings are without food for one - two hours, the hungrier they are, the less they sleep. Impulses of the hunger receptor suppress the breaking effect of sleep. Therefore, gaping reactions can be released more easily and sometimes more strongly in hungry animals. It has, however, nothing to do with the damming up of excitation in the centre but takes place within the afferent system. While even in hunger the releasing effect of a single stimulus remains unchanged the function of the releasing mechanism changes in the sense that it becomes more and more unselective. Finally normally quite inadequate stimuli become effective. Young in which gaping during the period of hunger is released uninterruptedly, behave just as those animals which are not stimulated during this time. This proves that the unselectivity of the I.R.M. in hunger is not due to charges in the instinctive act centre. 6. Older animals which possess the instinctive act of crouching show this when they are adapted to a gaping releasing stimulus thereby showing a change of motivation. This remains as long as the adaptation lasts. 7. Finally from the basis of the new results the conception of the reflex and automatic elements i.e. the instinctive act are criticised