36 DIGESTION AND FOOD. 



bones, in combination with phosphate of lime, as an amor- 

 phous, granular, earthy principle, destined to contribute to 

 the solidity of the skeleton. In invertebrate animals, the 

 carbonate of lime forms the basis of the solidifying prin- 

 ciples of shells, scales, &c. 



VI. CARBONATE OF SODA is found in the blood, lymph, saliva, 

 and other secretions of herbivorous animals, and in smaller 

 proportions in man, and other omnivorous and carnivorous 

 animals. The quantity, if any, under many circumstances, is 

 with difficulty appreciated, from the readiness with which the 

 salt is formed during the incineration of organic matters. 



VII. CARBONATE OF POTASH, like the preceding salt, obeys 

 much the same laws, and is found under similar circumstances. 

 Potash is a most essential element in the food of man and 

 animals. It is found largely in many plants. Regarding the 

 origin of the alkaline salts, we find that they are partly intro- 

 duced as such with the food, and partly the result of chemical 

 changes within the body. 



"Lehmann found, by experiments upon his own person, 

 that within thirteen minutes after taking half an ounce of 

 lac'tate of soda, the urine had an alkaline reaction. He also 

 observed that, if a solution of lactate of soda were injected 

 into the jugular veins of a dog, the urine became alkaline at 

 the end of five, or, at the latest, of twelve minutes. The con- 

 version of these salts into carbonates takes place, therefore not 

 in the intestines, but in the blood. The same observer found 

 that, in many persons living on a mixed diet, the urine be- 

 came alkaline in two or three hours after swallowing ten 

 grains of acetate of soda. These salts, therefore, on being 

 unreduced into the animal body, are decomposed. Their 

 organic acid is destroyed, and replaced by carbonic acid; and 

 they are then discharged under the form of carbonates of 

 soda and potass." 



