496 NUTRITION. 



blood, sebaceous matter, and sometimes in the urine. It exists as a normal constituent in 

 the urine of some herbivora, but not in the carnivora or in man. It is most appro- 

 priately considered immediately after the phosphate of lime, because it is the salt next 

 in importance in the constitution of the bones and teeth. In these structures it exists 

 intimately combined with the organic matter, under the same conditions as the phos- 

 phates, and it has analogous functions. In the fluids it exists in small quantity and is held 

 in solution by virtue of free carbonic acid and the chloride of potassium. 



The carbonate of lime is the only example of an inorganic proximate principle exist- 

 ing uncombined and in a crystalline form in the body. In the internal ear it is found in 

 this form and has some function connected with audition. 



Table of Quantities of Carbonate of Lime. 



Parts per 1,000. 



In Bone, human (Berzelius). 1 13'00 



" " " (Marchand) 102-00 



" " " (Lassaigne) 76'00 



" Teeth of an infant one day old \ ( 140'00 



" Teeth of an adult V Lassaigne < 100-00 



" Teeth of an old man, eighty-one years i ' lO'OO 



" Urine of the horse (Boussingault) 10*82 



Origin and Discharge of Carbonate of Lime. Carbonate of lime is introduced into 

 the body with our food, held in solution in water by the carbonic acid which is always 

 present in small quantity. It is also formed in the body, particularly in the herbivora, 

 by a decomposition of the tartrates, malates, citrates, and acetates of lime contained in 

 the food. These salts, meeting with carbonic acid, are decomposed, and the carbonate 

 of lime is formed. It is probable that, in the human subject, some of it is changed into 

 the phosphate of lime, and in this form is discharged in the urine ; but when and how 

 this change takes place has not been definitely ascertained. 



Carbonate of Soda. This salt is found in the blood and saliva, giving to these fluids 

 their alkalinity ; in the urine of the human subject, when it is alkaline without being 

 ammoniacal ; in the urine of the herbivora ; and in the lymph, cephalo-rachidian fluid, and 

 in bone. The analyses of chemists with regard to this substance are very contradictory, on 

 account of its formation during the process of incineration ; but there is no doubt that it 

 is found in the above situations. The following table gives the quantities which have 

 been found in some of the fluids and solids : 



Table of Quantities of Carbonate of Soda. 



Parts per 1,000. 



In Blood of the ox (Marcet) 1'62 



" Lymph (Nasse) 0'56 



" Cephalo-rachidian fluid (Lassaigne) 0'60 



" Compact tissue of the tibia in a male of 38 years (Valentin) 2*00 



" Spongy tissue of the same (Valentin) 0-70 



Function of Carbonate of Soda. This substance has a tendency to maintain the 

 fluidity of the albuminoid constituents of the blood, and it assists in preserving the form 

 and consistence of the blood-corpuscles. Its function in nutrition is rather accessory, 

 like that of chloride of sodium, than essential, like the phosphate of lime, in the con- 

 stitution of certain structures. 



Origin and Discharge of Carbonate of Soda. This substance is not introduced into 

 the body as carbonate of soda, but it is formed, as is the carbonate of lime in part, by a 

 decomposition of the malates, tartrates, etc., which exist in fruits. It is discharged occa- 

 sionally in the urine of the human subject, and a great part of it is decomposed hi the 



