i.\ PSYCHO-PHYSICAL PHENOMENA 471 



Other authors (Eabl-Euckhard, Demoor, Querton, and others) 



regarded the moniliform irregularities of the dendrites as ;i, sign 

 of shortening ;i.l'trr fatigue, which interrupts the ueuronic associa- 

 tions and proiluces sleep. But it \\as shown hy Stel'anowska th;it 

 the nionilil'onu appearance of the dendrites is a pathological 

 s\ niptoiii, and cannot he 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 

 kataholites 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 

 hypiiphysis (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 

 largelv 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 

 fbinls) 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 ni'ccssary 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 Hrunelli, sleep is a phenomenon 

 of adaptation which is developed in the struggle for existence. 



