vi PREFACE 



between our bodies and a motor-car : the early 

 cars had all to be started by a laborious winding- 

 up process, equivalent to will power; the later, 

 by what is known as the self-starting process, 

 electricity in place of muscle. All the unseen 

 intricate work of our bodies, the chemical changes 

 we call metabolism, growth, renewal, and excre- 

 tion of waste, has to be done by self-starters, 

 almost outside consciousness or control. The 

 parallel may be extended, for each endocrine 

 gland is an individual motor, and discharges its 

 own particular variety of petrol into the big 

 motor, the body : on the proper mixture of these, 

 and on their healthy formation, life and health 

 depend ; again, the brakes and accelerators of our 

 bodies are largely vegetative, for they depend on 

 endocrine co-ordination, without which the engines 

 would soon race and wear themselves out or go so 

 slow that life would cease. We can without doubt 

 trace the greater part of the unconscious vegeta- 

 tive business of life back to the influence of these 

 glands, but still the mystery of life, the initial 

 force, the power behind the throne remains un- 

 solved ; to get a glimpse of this we must try to 

 visualize the great unseen force that governs the 

 Universe, that controls the movements of the 

 amoeba, that directs the courses of the sun, the 



