INORGANIC SUBSTANCES. 107 



The quantity of chloride of sodium contained in the Urine is liable to very 

 great variations, being greatly augmented when an excess of salt has been in- 

 gested either in food or in water ; and it is obvious that it is one of the offices 

 of the kidney to filter off, so to speak, the superfluity of this substance from the 

 blood. Chloride of sodium finds its way into the system, as a constituent of 

 almost all articles both of vegetable and animal diet; it is also contained, though 

 in small proportion, in most of the water which is used as drink ; and by most 

 races of man, it is used in considerable amount as a condiment. It seems pro- 

 bable, however, that the quantity which is really required is usually supplied 

 by the ordinary diet; and there are numerous tribes which subsist in health 

 and vigor without any additional source of it. Probably the inhabitants of 

 inland countries may stand in greater need of salt, than the dwellers on the 

 seaboard ; since the plants grown in the latter situation contain a much larger 

 amount of this saline derived from the atmosphere, than do those raised at a 

 great distance from the ocean. 



83. That a small quantity of the Alkaline Carbonates (especially of carbon- 

 ate of soda) exists in ordinary Blood, though its presence was denied by Ender- 

 lin, is now generally admitted by Chemists. Lehmann states the proportion, 

 as the mean of ten analyses of ox-blood, at 0.16 per cent. Since free carbonic 

 acid is undoubtedly present both in venous and arterial blood, it has been main- 

 tained that its soda must be in the condition of a bicarbonate, since the ordinary 

 carbonate of soda cannot remain as such in the presence of a free acid ; but the 

 soda-salt, whatever be its nature, is probably united so intimately with the pro- 

 tein-compounds, that its ordinary modes of combination are greatly modified. 

 The carbonate and bicarbonate of soda (particularly the latter) have a special 

 power of rendering Albumen soluble ; and their presence in large quantity has 

 the effect of impeding or altogether preventing the coagulation of the Fibrin, 

 apparently through their power of chemically dissolving it. The alkaline car- 

 bonates in the blood are probably for the most part not introduced as such, but 

 result from the decomposition of the lactates ( 49) and of other salts formed 

 by organic acids, a considerable amount of which must be ingested in the food 

 of herbivorous animals. And one, at least, of their functions within the system, 

 is to supply a base for the acids which are generated within it; these acids being 

 produced (as in the case of phosphoric and sulphuric acids) during the disinte- 

 gration of the tissues, and forming, with bases, neutral salts which are speedily 

 eliminated from the system by the kidneys ; or (as in the case of lactic acid) 

 being developed by the metamorphosis of compounds which may have never 

 formed part of the living tissues, and being only united temporarily with the 

 base, to be reduced by the respiratory process, leaving the base in its original 

 state of combination with carbonic acid. The following, according to Prof. 

 Liebig, are among the important purposes which are served by the alkalinity of 

 the Blood. By its means, the chief constituents of the blood are kept in their 

 fluid state ; the extreme facility with which the blood moves through the 

 minutest vessels is due to the small degree of permeability of the walls of these 

 vessels for the alkaline fluid. The free alkali acts as a resistance to many 

 causes, which, in the absence of the alkali, would coagulate the albumen. The 

 more alkali the blood contains, the higher is the temperature at which its albu- 

 men coagulates ; and with a certain amount of alkali, the blood is no longer 

 coagulated by heat at all. On the alkali depends a remarkable property of the 

 blood, that of dissolving the oxides of iron, which are ingredients of the color- 

 ing matters of the blood, as well as other metallic oxides, so as to form perfectly 

 transparent solutions. The free alkali serves also to promote the combustion 

 of organic compounds, which in its presence acquire a power of combining with 

 oxygen that they do not possess alone at ordinary temperatures ; thus milk- 

 sugar and grape-sugar, in presence of a free alkali, and with the aid of a gentle 



