62 USE OF COMMON SALT. 



a more or less extensive change. But these changes are altogether insig- 

 nificant when compared with those great metamorphoses which the nu- 

 trient material passes through after it has been absorbed from the digest- 

 ive cavities ; and doubtless, at the most, they are only mere subdivisions, 

 of which the splitting of the sugar or starch atom into lactic acid may be 

 taken as the type, or mere unions with water, of which the passage of 

 cane sugar into milk sugar is an example. 



The gastric juice, therefore, not only dissolves, but also, in an incipient 

 Production of an< l indirect manner, modifies the food. Protein bodies and 

 peptones. gelatinous matters yield substances after its action of the 

 same composition as their own, but with different physical and chemical 

 properties, being readily soluble in water, and even in diluted alcohol, and 

 not forming insoluble compounds with metalline salts. By Lehmann, 

 who has examined these substances, they have been designated as pep- 

 tones ; and since they may arise without the evolution or absorption of 

 any gas, and the quantity of sulphur they contain is the same as that in 

 the bodies from which they were derived, he infers that the action is real- 

 ly an assimilation of water, the other ingredients remaining unchanged. 



Turning our attention now to the origin of the gastric juice, it is inter- 

 esting; to observe the economical manner in which its hydro- 

 Use and man- . . . , . 

 agement of chloric acid element is managed. To the proper understanding 

 jommon s t. Q ^j^ ^ j s necessary to anticipate what will have to be more 

 fully considered in describing the bile, a uniform ingredient of which is 

 the oxide of sodium, or soda. The hydrochloric acid of the gastric juice 

 and the soda of the bile are derived from the same source common salt, 

 which is either present in the food, or purposely added as a condiment. 

 It undergoes decomposition easily, yielding the two products specified, 

 that is, hydrochloric acid and soda, and is readily formed by the reunion 

 of these substances. 



There exists in the action of the kidneys a special provision for prevent- 

 ing the quantity of chloride of sodium present in the blood from rising 

 over 41 parts in 10,000. This, of course, controls the amount diffused 

 through the tissues. The necessity of such a regulation becomes appar- 

 ent when we consider that the rate of the solubility of albumen and ca- 

 sein in water is governed by the presence of that substance, as is also the 

 quickness with which the coagulation of fibrin takes place, and the re- 

 pair of the waste of the muscles. 



Common salt introduced into the system undergoes decomposition, 

 furnishing hydrochloric acid to the gastric juice, and soda to the bile. 

 Considering the large quantity of these secretions produced in a short 

 space of time, it is clear that the drain of common salt must be great 

 not less than a third of an ounce a day ; yet the quantities consumed, at 

 most, are only small. 



