Internal Stimuli 2 1 



change of environment. Internal stimuli result 

 in part from energy derived from the sensory 

 organs of ligaments, muscles, and other struc- 

 tures in contraction, pass by afferent fibres to 

 motor areas of the cerebral cortex, and by re- 

 leasing a portion of their potential energy 

 bring " motorial " or " kinaesthetic " sensations 

 into play. Beyond this various biochemical 

 stimuli known as " hormones " are formed in 

 various glands of our bodies; they enter the 

 blood stream and activate among other struc- 

 tures the instinctive sensori-motor elements of 

 the central nervous system. It seems possible 

 that some of these hormones, by exciting the 

 basal nervous matter of a new-born infant's 

 instinctive elements, may lead to the move- 

 ments which guide his limbs to seize and 

 direct the nipple of his mother's breast to his 

 mouth. 1 



Instinct is in fact a fundamental property of 

 certain inherited forms of living matter, as is 

 demonstrated by the behaviour of some of the 



1 An Essay on Character in Relation to the Emotions and 

 Instincts, Science Progress, No. 36, April, 1915, pp. 683-685, an 

 Introduction to the Study of the Endocrine Glands and Internal 

 Secretions. By Sir Edward Schafer. 



