238 THE HUMAN SPECIES 



actual anastomosis between nerve-cells, but modern observers 

 have shown that the branches of the neurones and the dendrites 

 have free ends, which are not permanently attached to, but are 

 in intermittent contact with one another, so that sleep comes 

 on when the prickle-like dendrites of the ganglion-cells contract 

 themselves into minute club-shaped swellings and break contact 

 with the branches of the neurites. 



The condition of hypnotism, in which there is marked 

 cessation of excitability and dissociation either over the whole 

 cortex or particular parts, is in many respects identical with 

 sleep. That animals, as well as men, are susceptible to hypno- 

 tism was demonstrated in 1646 by Kircher's experiment on a 

 hen which remained motionless with its eyes fixed on a chalk 

 line on the ground. Czermak, who has made considerable 

 researches upon hypnotism in animals, performed the experi- 

 ment on the hen without a chalk line, " fixing " it instead with 

 a splinter of wood on the beak. Both these cases are examples 

 of hypnosis by fixation. The "fascination of the victjm," 

 sometimes seen among insects, is not so much an artifice as a 

 hypnotic paralysis evoked by fear. Preyer distinguishes in 

 this process a cataplexy (terror effect, enchantment) apart 

 from the true hypnosis, and gives as an instance the snake and 

 its prey. 



VIII. Cranial Nerves and Sense-organs. 



The physiology of the senses cannot be separated from the 

 consideration of the nervous system, for we cannot conceive of 

 the brain apart from the sense-organs, nor the latter without the 

 nerve communications with the brain. 



Unfortunately, the comparative physiology of the senses has 

 not kept pace with the comparative anatomy, partly because 

 many animals are so imperfectly organised that they do not 

 seem to respond to such stimuli as we can devise, partly because 

 it is exceedingly difficult to interpret the reaction which is 

 evoked. 



(a) Sense of Smell. 



Here we are soon confronted by the absence of comparative 

 physiology, for although we can trace olfactory organs from 



