WORKSHOPS AND LABORATORIES 169 



or tongue forcing a prepared charge or bolus of food from 

 the mouth through the threshold of the pharynx, where 

 it is launched on its journey to the second alimentary 

 factory or workshop — the stomach. 



Just before closing this account of the various opera- 

 tions carried on in the mouth, there is one other matter 

 which requires emphasis. We touched upon certain of 

 the nerve stations which are scattered over the surface of 

 the tongue and mouth and from which taste and touch 

 messages are dispatched. There are also those end 

 stations which keep the central nervous system informed 

 as to the temperature of the food and drink as it enters the 

 mouth. Mention must be made of still another system 

 of nerve receivers and signallers, placed around the 

 sockets of teeth and also within the pulp which fills the 

 natural central cavities. From these dental nerve stations 

 pressure messages are dispatched which keep the muscles 

 of mastication informed as to strains and stresses which 

 are falling on the teeth and from which they can regulate 

 the amount of pressure to be applied. Healthy teeth 

 seem to us to give rise to no sensation ; we are not 

 conscious of messages arising in or near them. If, 

 however, their pulps become exposed, then, as every one 

 knows, they can be the source of excruciating messages. 

 Here again we meet with another of Nature's methods of 

 levying fines for neglect. 



