WORKSHOPS AND LABORATORIES 163 



placed " taste-buds " which sample every particle which 

 crosses the lips ; messages are instantly dispatched to 

 both higher and lower nerve centres in the brain and 

 brain stem, keeping them in touch with what is 

 happening in the mouth. Even before the food has 

 passed the lips it has been sampled by the nose and smell 

 messages have been dispatched to the brain, where they 

 and the taste messages mingle and help, if they be 

 agreeable, to give rise to that feeling we name appetite. 

 The minute taste-buds, the transmitting stations for taste 

 messages, are scattered on the upper surface of the tongue, 

 chiefly towards its hinderpart, its base or root. The 

 juices of the food in the mouth actually penetrate the 

 coats of the taste transmitters and dispatch their messages, 

 apparently by means of chemical reactions. The taste- 

 buds are placed on the tongue because in chewing and 

 swallowing they are thus brought in full contact with 

 everything taken into the mouth. In the mouth food is 

 wholly under our control ; when it enters the throat or 

 pharynx, as happens when we swallow, it passes into the 

 charge of a machinery over which we can exercise no 

 influence. It is on the threshold between the mouth and 

 pharynx — between the voluntary and involuntary chambers 

 — that Nature has planted the most powerful of her taste 

 transmitters ; the majority are placed on the root of the 

 tongue, on the edge of the threshold ; some also on the 

 palate or lintel of the doorway. Before we can fully 

 relish the taste of food it has to pass the threshold which 

 takes it from our control. Nature, you see, has made 

 as certain as is possible that fuel for the human machine 

 will be used and not abused. 



The appetite of a motor cycle is strictly limited by the 

 size of the petrol tank and the dimensions of the jet aper- 

 ture in the carburettor. An indicator tells the driver, as he 

 fills the tank, when the limit of its capacity is reached. The 

 human machine has also its indicator ; when the stomach 

 is filled there rises over us a feeling of repletion, but the 

 exact mechanism which gives origin to this feeling is not 

 yet understood. The stomach is not a rigid chamber, we 



