178 THE ENGINES OF THE HUMAN BODY 



from controlling centres in the medulla. But even when 

 these pathways are cut, local mechanisms can still carry 

 on transport duty, although indifferently. Then in the 

 loose binding tissue, between the lining and muscular 

 coats of the oesophagus, there are other nerves sending 

 fibres to end in contact and touch transmitters and form- 

 ing part of an elaborate touch-button machinery. In that 

 same tissue, too, lie numerous little .factories or glands 

 for the production of a fluid to lubricate the lining of the 

 oesophagus and facilitate the passage of food boluses. 

 Nature forgets no necessary detail. Mention need hardly 

 be made of the arteries and veins which maintain a steady 

 circulation of blood through its capillary fields and supply 

 the muscle spindles with oxygen and fuel and a means of 

 carrying away their waste products. 



We have been merely enumerating the parts of the 

 oesophageal machinery ; we are now to see these parts 

 in operation, transporting a bolus of food towards the 

 stomach. The instant that a bolus has been pushed 

 through the doorway leading from the pharynx and that 

 doorway has closed, we see a ring of contraction form 

 behind the bolus and commence to creep slowly down- 

 wards, forcing the bolus in front of it. The bolus 

 on entering the oesophagus has touched a " button," and 

 the ring of contraction is the result. As the bolus is 

 driven forwards it comes in contact with a succession of 

 such buttons, with the result that it is kept moving 

 onwards. Not only so ; a ring of relaxation precedes 

 the bolus and eases the passages. The ring of relaxation 

 which heralds the advance of a bolus is, as Bayliss and 

 Starling discovered, produced by the same touch-button 

 mechanism as controls the propelling constriction ring. 

 Every inch in the advance of a bolus means that millions 

 of spindle engines have been duly started and stopped 

 by an automatic controlling mechanism. 



I have dealt rather fully with the transport system of the 

 oesophagus because everywhere along the alimentary canal 

 we shall find that a similar mechanism is employed. It is 

 indeed a complex machinery representing many millions 



