The Body-Machine and Its Work 



superfluous) do not develop. On the other hand, a few people 

 have thirty-six teeth, and when we turn to the monkeys we find 

 that some of them have this number. We are, in faet, slowly 

 shedding our teeth, in fours, along the corridors of time, and it 

 may be that in the distant future man will be toothless. Per- 

 haps, however, a fresh enthusiasm for physical vigour will save 

 the race from any such degeneracy. 



But our "grinding-stones" are only part of the mechanism 

 of the mouth. As soon as the grinding begins three pairs of 

 glands pour saliva into the food. Here again we have an auto- 

 matic nervous machinery of a remarkable kind, for, as every- 

 body knows, the mere sight of food may set the glands at work, 

 or "make your mouth water." In the glands themselves the 

 microscopic cells which make the saliva are such remarkable 

 chemical machines that we cannot yet understand them. They 

 not only help to make a soft pulp of the food the saliva is 99 

 per cent water but they pour into it certain chemicals which 

 begin the digestion of starchy food, converting it into a kind of 

 sugar. That is one of the reasons for thorough "mastication." 

 One must not suppose that it does not matter, since the food 

 is so short a time in the mouth that there cannot be much chemical 

 action on it. The chemical action of the saliva goes on, for half 

 an hour or more, while the food is in the stomach. A great deal 

 of illness is due to neglecting to mix plenty of saliva with our 

 bread, etc., before it leaves the mouth. 



3 



The Process of Digestion 



When teeth and salivary glands have done their work, and 

 the taste-buds on the tongue have had their moment of satisfac- 

 tion, the mouthful of pulp is swallowed. "Swallowing seems 

 such an easy and automatic act that we are quite unaware of 

 the elaborate system of signals, side-shunts, and level-crossings 

 which have to be manipulated to permit the busy traffic of the 



