254 HUMAN BIOLOGY 



especially sensitive to this proprioceptive stimulation by 

 passive stretch. This antigravity reaction of the muscles 

 themselves is reinforced by adjuvant reflexes operated by 

 pressure of the foot upon the ground. The whole many- 

 muscled reflex is further modified by reflexes originated by 

 two tiny gravity organs lying in the bony wall of the skull, 

 and forming part of the inner ear, though not themselves 

 auditory. These Kttle sacs contain small crystaHine "stones" 

 loosely attached to sensitive nerve patches. According 

 to the position of the head the stones press or drag upon 

 the nerve bed in this or that direction and to this or that 

 degree. These cranial gravity sacs have through their 

 nerves and the lower nervous centers the power of modifying 

 the gravity reflexes of the antigravity muscles. 



It is abundantly shown by experiment in the higher 

 animals that the standing posture and stepping, walking 

 or running can be executed after destruction of all the 

 higher parts of the brain and certainly after removal of 

 all that part which may be termed the "mental organ." 

 Not only does the purely reflex animal stand and step, 

 but it can when displaced from the erect position reflexly 

 regain it and restore itself, head, body and limbs and all 

 to that posture. A remarkable manoeuvre exhibited by 

 the cat is that when inverted and let fall from a short 

 height, it rights itself in the air and alights on its feet. 

 This manoeuvre is executed perfectly by reflex action after 

 removal of the animal's entire higher brain; cinemato- 

 graph analysis of the act shows that it is then performed 

 exactly in the same way. Observations upon human infants 

 with congenital non-development of the higher brain have 

 revealed in them also righting reflexes resembhng those 

 of animals. 



To these reflexes of habitual attitude and locomotion 

 can be added a number which bear the purpose of self- 

 protection. Thus the reflex quadruped will, if it hurts 

 one foot, go on three legs with the hurt foot held up out 

 of further harm's way. The ear of the purely reflex cat will 

 flick and throw ofl' the fly which settles there, not less 

 promptly than does that of a normal cat. So too the dog 

 scratches itself, grooming its coat by a rhythmic movement 



