224 NUTRITIONAL PHYSIOLOGY 



salts of the teeth at points where the enamel has been 

 chipped or worn away, or where it fails to meet the gum. 

 The dissolving of the lime-salts leaves a soft and perishable 

 organic structure which readily undergoes true decay. 

 Every tiny deposit of sugar in the crevices of the teeth may 

 soon become a focus of acid production and a center of 

 disintegration. The popular impression that plain sugar 

 is not so hurtful as sugar mingled with other substances in 

 candy has this basis : pure sugar is so readily dissolved by 

 the saliva that it is not likely to remain long clinging to the 

 teeth. On the other hand, sugar which is mixed with fatty 

 materials like chocolate may be sealed into crannies or 

 retained under the edge of the gum with unfortunate effect. 

 One who is bound to eat much candy should be willing to 

 exercise unusual care to free the teeth from the remains, 

 and may, in spite of his pains, have periodical days of 

 reckoning at the dentist's. 



Food Accessories. It is perhaps unnecessary to enlarge 

 upon the service of those compounds which are classed 

 under this head. The double value of the extractives of 

 meat which favor digestion both because of the flavors 

 which they develop and because of their direct action upon 

 the stomach wall has been sufficiently emphasized. The 

 various condiments are believed to have a similar signifi- 

 cance. So far as they season the food so as to make it 

 more acceptable, they must evidently promote secretion. 

 Their power to call forth the gastric juice by a purely local 

 effect is not so well established, but they are known to in- 

 crease the blood-flow in the mucous membrane, which 

 must help to sustain the local activities. 



Tea and Coffee. These beverages owe what limited 

 food value they have to the cream and sugar usually 

 mixed with them. They give pleasure by their aroma, but 

 they are given a peculiar position among articles of diet by 

 the presence in them of the compound caffein, which is 

 distinctly a drug. It is a stimulant to the heart, the kid- 

 neys, and the central nervous system. It is chemically 

 related to uric acid, but is not known to yield this incon- 



