244 USE or salt — digestion. 



digestible itself, but likewise produces a similar effect 

 on the substances with which it is mixed. These 

 two conditions may be well observed, on comparing 

 together good melted butter, with that which has 

 been allowed to " oil." 



631. Common salt is a necessary ingredient of all 

 good food. Its use in the preparation of food is evi- 

 dent from the preceding remarks ; it is also valuable 

 in its preservation, acting as an antiseptic, and pre- 

 venting it from undergoing fermentation or change. 

 Salt is further important as aiding digestion, to which 

 both the soda and muriatic acid it contains are ne- 

 cessary (608). 



6'S2. The effects of various condiments and spices 

 on the appetite are very remarkable; stimulating it, 

 and sometimes in a very beneficial manner. The prin- 

 ciples upon which these substances act is very ill un- 

 derstood, and cannot be satisfactorily explained by 

 reference to ordinary chemical facts ; indeed, it can 

 hardly be otherwise till the chemistry of digestion is 

 more fully understood. 



633. The phenomena of digestion in some respects 

 resemble those of fermentation. The substances used 

 as food, are for the most part all very liable to 

 undergo fermentation ; and the nature of the change 

 thus brought about depends wholly upon circum- 

 stances. Any derangement in the process of diges- 

 tion, may permit some other change to commence, 

 and- the system must then be immediately thrown 

 out of order. A very great number of diseases may, 



