PSYCHO-PHYSICAL PHENOMENA 471 



Other authors (Babl-Kuckhard, Demoor, Querton, and others) 

 regarded the moniliforin irregularities of the dendrites as a sign 

 of shortening after fatigue, which interrupts the neuronic associa- 

 tions and produces sleep. But it was shown by Stefanowska that 

 the moniliform appearance of the dendrites is a pathological 

 symptom, and cannot be related to normal sleep. 



Finally, according to Lugaro, in active states the only normal 

 mobility of the neurones is a slight movement of the terminations; 

 the varicosity of the dendrites is a pathological phenomenon due 

 to fatigue or intoxication ; the characteristic change in sleep is a 

 general expansion of the tiny spines or gemmules of the dendrites ; 

 the retraction of these serves to isolate certain systems of neurones, 

 to secure the momentary autonomy of the psychical associations, 

 and thus to concentrate the attention upon certain groups of 

 sensations or images. Nor does this exhaust the pack of hypo- 

 theses : according to Lugaro the expansion of the dendritic spines 

 in sleep may be the effect either of the autotoxic action of the 

 katabolites or of the inactivity of the nerve elements. Imagina- 

 tion is a precious gift in science when it serves to propound new 

 problems and promote new researches ; but its value is negligible 

 when it is employed to build castles in the air from hypotheses 

 which make a pretence of solving recondite physiological 

 problems. 



The same may be said of all the other partial theories of sleep, 

 which are founded on a set of physiological or pathological facts, 

 to which they give an arbitrary interpretation. Such, for 

 instance, is the secretory theory, a reflex from the modern dis- 

 coveries on the endocrinal glands, particularly the thyroid and 

 hypophysis (Salmon, 1904-5) ; or the osmotic theory of Devaux 

 (1906), according to which sleep is due to dehydration, owing to 

 the increased viscosity of the blood ! 



None of the above theories, in attempting to explain the 

 alternation of sleeping and waking, have taken into account the 

 variations in its rhythm presented by different animals, which are 

 largely due to the needs of defence, environmental conditions, the 

 necessary hunt for food, etc. Why are some species and genera 

 of animals (dogs, cats) able to sleep at any moment; why do 

 others (rodents, herbivora) sleep very lightly; why have some 

 (birds) the briefest possible sleep although their respiratory 

 exchanges are extraordinarily active ; why do some sleep by day 

 and wake by night ? 



H. Foster (1900) and Brunelli (1903), from a high biological 

 standpoint, insisted that in order to solve the problem of sleep it 

 is necessary to study its genesis in the phylogenetic scale, and not 

 rest content with analysing it in man " within the narrow limits 

 of the cranium." According to Brunelli, sleep is a phenomenon 

 of adaptation which is developed in the struggle for existence. 



