54 INORGANIC PROXIMATE PRINCIPLES. 



the administration of sulphur or a sulphuret. 1 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 at once with the alkaline bases, displacing the weaker acids with 

 which they were previously combined, and thus contributes indirectly 

 to the general acid reaction of the excreted fluids. 



The foregoing substances constitute the most important of the in- 

 organic proximate principles of the animal body. They are distin- 

 guished, as a class, by their comparatively simple chemical composition, 

 by their external origin, and by the part which they take in the constitu- 

 tion 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 ; and of the sodium biphosphate pro- 

 duced from the neutral phosphate, by the action of an organic acid of 

 internal origin. The greater part, however, of the proximate principles 

 belonging to this class are introduced with the food, and taken up 

 by the animal tissues and fluids, in the form under which they exist 

 in external nature. The lime carbonate of the bones, for example, and 

 the sodium chloride of the blood and the tissues, are the same sub- 

 stances as those met with in calcareous rocks, or in solution in sea 

 water. 



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

 rule, from any marked chemical changes. Some of them, such as the 

 lime and magnesium phosphates, are mostly deposited in the solid parts, 

 and are renewed very slowly, contributing principally 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 introduced and discharged daily in considerable abund- 

 ance, passing rapidly through the system, and playing an important 

 part in the phenomena of solution and transudation. Others still, such 

 as the alkaline phosphates and sulphates, are partly formed in the body 

 by the process of oxidation, and appear in the urine as a residue from 

 the decomposition of other proximate principles. 



Principally, however, the inorganic substances are reabsorbed by the 

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

 unchanged with the excretions. The importance of this character will 

 become fully manifest when we see how different are the relations 

 exhibited by the proximate principles of other groups. The inorganic 

 substances do not, for the most part, participate directly in the chemical 

 changes going on in the body ; but rather serve by their presence to 

 enable those changes to be accomplished, in the other ingredients of the 

 animal frame, which are necessary to the process of nutrition. 



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



