INORGANIC SUBSTANCES. 37 



the organic ingredients of the food, which is not wholly accounted for 

 in the excretions. The most reliable estimates, in this respect, are as 

 follows : 



AVERAGE DAILY QUANTITY OF HYDROGEN 



Introduced in organic combinations with the food . . .40 grammes. 

 Discharged " " excretions . . _6 



Residue unaccounted for 34 " 



Thus not more than fifteen per cent, of the quantity introduced is 

 discharged in the organic ingredients of the excretions. But hydrogen 

 is not exhaled from the body in notable quantity in a free state, nor in 

 any other form of inorganic combination except water. The intestinal 

 gases contain habitually hydrogen and carburetted hydrogen in the 

 proportion of about thirty-eight per cent, of their volume.* The abso- 

 lute quantity of these gases in the normal condition has not been deter- 

 mined ; but it is evidently quite insufficient to account for the missing 

 hydrogen, 34 grammes of which would occupy, in the gaseous form, a 

 space of 379 litres. The surplus hydrogen must therefore be discharged 

 in the form of water or watery vapor. The estimates given above 

 indicate that not far from 300 grammes of water are daily produced in 

 the body in this way. One important class of the ingredients of the 

 food, hereafter to be described, already contain hydrogen and oxygen in 

 the relative quantities necessary to form water ; and, when decomposed 

 in the system, they may readily yield these elements in the required 

 proportions. 



Furthermore, although it has not yet been proved, in any particular 

 case, that more water is discharged from the system than can be 

 accounted for by that introduced, yet a comparison of the average 

 results obtained by different observers always tends to show a surplus 

 of water discharged, from 200 to 500 grammes over and above that in- 

 troduced with the food and drink. The quantity of water, however, 

 thus produced in the body is small in comparison with that introduced 

 and discharged under its own form. 



While in the interior of the living body, water is useful principally 

 by its physical properties. It is the universal solvent for the ingre- 

 dients of the animal fluids, holding them in solution either directly 

 or by the aid of other substances which are themselves soluble. It thus 

 enables the elements of the food to find their way into the circulating 

 fluid, and into substance of the .organs. It permeates the membranes 

 and brings into contact with each other the inorganic and organic mate- 

 rials of various parts, and enables them to assume new forms by mutual 

 reaction. In this way it is subservient to the phenomena of absorp- 

 tion, transudation, exhalation, chemical union and decomposition, which 

 make up the nutritive functions of the animal frame. 



* Marchand : Journal fiir praktische Chemie. Leipzig, 1848. Band XLIV., p. 10. 

 Huge: Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften. "NVien, 

 1862. Band XLIV., p. 739. 



