\ 

 48 PHYSIOLOGICAL CHEMISTRY. 



in the body, during the decomposition of albuminous matters, by oxi- 

 dation of their sulphur. This is confirmed by the fact that the quantity 

 of sulphuric acid in the sulphates eliminated by the kidneys is increased 

 by a flesh diet, and also by the administration of sulphur or a sulphuret.* 

 Dr. Parkes estimates the quantity of sulphuric acid thus produced in 

 the system as about double that taken in the form of sulphates with the 

 food and drink. It unites with the alkaline bases, displacing the weaker 

 acids with which they were combined, and thus contributes indirectly 

 to the general acid reaction of the excreted fluids. 



The foregoing substances are the most important of the inorganic 

 ingredients of the body. They are distinguished from the organic in- 

 gredients by their comparatively simple chemical composition, by their 

 external origin, and by the part which they take in the constitution and 

 nourishment of the animal frame. They are derived for the most part 

 from without, being taken directly from the materials of the inorganic 

 world. There are some exceptions to this rule ; as in the case of the 

 alkaline carbonates formed in the body by decomposition of the salts 

 of the vegetable acids ; of the sodium biphosphate produced from the 

 neutral phosphate by the action of an organic acid, and of the phos- 

 phates and sulphates formed by the process of oxidation. But the 

 greater part of the substances belonging to this class are introduced 

 with the food, and absorbed by the animal tissues and fluids, in the 

 form under which they exist in external nature. The lime carbonate 

 of the bones, and the sodium chloride of the blood and the tissues, are 

 the same substances as those met with in calcareous rocks, or in sea 

 water. 



In the process of internal nutrition they are exempt, as a general rule, 

 from chemical change. Some of them, such as the lime and magne- 

 sium phosphates, are mostly deposited in the solid parts, and are re- 

 newed but slowly, contributing mainly to the physical properties of the 

 tissues, and taking a comparatively small share in the actions of repair 

 and waste. Others, such as water and the alkaline chlorides, are intro- 

 duced and discharged in abundance, passing rapidly through the system, 

 and playing an important part in the phenomena of solution and tran- 

 sudation. Others, such as the alkaline phosphates and sulphates, when 

 formed in the body by oxidation, appear in the urine as a residue from 

 the decomposition of other substances. 



The larger proportion, however, of the inorganic matters are reab- 

 sorbed from the tissues in which they were deposited, and discharged 

 unchanged with the excretions. They do not, for the most part, par- 

 ticipate directly in the chemical phenomena of the living body ; but 

 rather serve to facilitate, by their presence, the necessary changes of 

 nutrition in other ingredients of the animal frame. 



* Neubauer und Vogel : Analyse des Hams. Wiesbaden, 1872, pp. 356, 357. 



