collectively form the brain. Now when an animal is 

 hungry, visceral impressions also ascend to the brain, and 

 so coming into contact with the sensory gangha, stimulate 

 the senses, and awaken the intellectual and motor activities. 



To sum up, we find the size and organisation of the 

 brain proportional to the development of the sense-organs. 

 As a result of increased brain organization we get increased 

 complexity of exit routes and more manifold and diiferen- 

 tiated muscular movements. Facility of locomotion widens 

 the range of sense-impressions, and so reacts again on the 

 brain, tending to develop it. Development is likewise 

 faciliated by the struggle for existence. It is noteworthy, 

 for example, that extinct bii-ds had a smaller cranial 

 capacity than existing birds. 



A striking illustration of the dependence of our mental 

 activity on sense-excitation is quoted by Bastian. A youth 

 was under treatment, whose skin " was completely insens- 

 ible, and that in respect to every kind of sensation. The 

 most powerful electric current, or a burning taper held to 

 the sMn, was not able to produce any pain, or even a sensa- 

 tion of touch. Almost all the accessible parts of the mucous 

 membrane of the body exhibited the same insensibility to 

 pain. Also all those sensations which are classed together 

 under the name of 'muscular sense' were entirely absent. 

 The patient, when his eyes were closed, could be carried 

 about round the room, his limbs could be placed in the 

 most inconvenient positions, without his being in any way 

 conscious of it. Even the feeling of muscular exhaustion 

 was lost. In addition there came on a complete loss of 

 taste and smell, bhndness of the left eye, and deafness of 

 the right ear. 



' ' In short, here was an individual whose only connection 

 with the outer world was limited to two doors of sense — 

 to his one (right) eye and his one (left) ear. Moreover, both 

 these remaining doors could at any time be easily closed, 

 and in this way it was possible to investigate the conse- 

 quences of completely isolating the brain from all external 

 stimulation through the senses. If the patient's seeing 

 eye were bandaged and his hearing ear were stopped, 

 after a few minutes the expression of surprise and the 

 uneasy movements which at first showed themselves, 

 ceased, the respiration became quiet and regular ; in fact, 

 the patient was sound asleep. Here, therefore, the possi- 

 bility of artificially inducing sleep at any time in a person 



