278 



THE PROPERTIES OF PROTOPLASM 



The ability of sodium bicarbonate, in equilibrium with carbonic 

 acid, to maintain the neutrality of its solutions is strikingly illustrated 

 by Henderson in the following way : " Suppose, for example, a solution 

 of 100 liters containing one kilogram of sodium' bicarbonate in 

 equilibrium with an atmosphere containing one gram of carbon 

 dioxide per liter. Let hydrochloric acid be added in successive small 

 portions to the solution. Further, let the solution be constantly stirred 

 and shaken, and let the experiment be conducted slowly, so that there 

 shall always be equilibrium between the carbonic acid in the solution 

 and in the atmosphere. Further, let the temperature be such that the 

 absorption-coefficient of carbon dioxide shall be 1.000. Then the 

 successive states of the solution will be approximately as recorded in 

 the following table. 



"From the beginning of the experiment until almost 250 grams 

 of hydrochloric acid have been added, neither alkalinity nor acidity 

 is double in intensity the values which obtain in a perfectly neutral 

 solution." "Such close approach to neutrality can be attained with 

 pure water only after elaborate and very difficult purification, yet in 

 the presence of carbonic acid it is the natural condition." 



In laboratory-glassware a mixture of disodium and monosodium 

 Phosphates would perhaps be almost as efficient as sodium bicarbonate 

 in preserving neutrality. In the body, however, they are not so 

 efficient as the bicarbonates because in the first place they are not 

 nearly so abundant and in the second place the elimination of the acid 

 phosphates which are formed in the neutralization of acids has to take 

 place by the relatively slow and roundabout channel of the kidneys, 

 while the elimination of carbon dioxide takes place rapidly through 

 ventilation from the lungs. 



Direct determinations by the potentiometric method have shown 

 that the proteins contribute just about one-fifth of the neutraliz ing- 

 power of the blood. In the tissues their proportional importance 

 in maintaining neutrality is probably greater, because they are present 

 therein in higher concentration than they are in the blood. 



