240 HUMAN BIOLOGY 



The Constancy oj the Neutrality of the Blood. The foregoing 

 edscription has repeatedly called attention to the release 

 of lactic acid and carbon dioxide (which in watery solution 

 forms carbonic acid) during muscular work. Besides these 

 and other acids which may be developed in the body, acid 

 foods may be eaten and absorbed and they also tend to 

 render the blood acid. On the other hand, the food may be 

 alkaline in reaction, or there may be a loss of acid from the 

 body by its secretion in the gastric juice, or the carbon 

 dioxide may be "pumped out" of the blood to a considerable 

 degree by prolonged deep breathing; each of these conditions 

 tends to render the blood alkaline. It is of the greatest 

 importance to the existence and proper action of the cells 

 that the reaction of the blood and tissue fluid shall not become 

 either acid or alkaline. If the blood becomes too acid, coma, 

 or unconsciousness, is likely to occur; if too alkahne, con- 

 vulsions may take place. If the fluid supplied to the heart 

 is too acid, the muscle relaxes and ceases to beat; if too 

 alkaline, it again ceases to beat, but usually stops in the 

 contracted state. These are only two examples out of many 

 that could be cited to show the dangers of a shift of the 

 chemical reaction of the blood too far away from the neutral 

 point between acidity and alkalinity. Within a narrow range 

 of variation the nervous system will operate perfectly, with 

 no signs of coma or spasmodic discharges, and the heart 

 will go on beating continuously. But the reaction must be 

 kept within that narrow range. 



The complete account of the mechanisms by which the 

 reaction of the blood is kept close to neutrality, in spite 

 of external and internal conditions which are constantly 

 acting to push the reaction away from that point, would 

 require elaborate and detailed consideration of highly 

 involved processes. We shall regard only the simpler aspects 

 of the mechanisms. Dissolved in the blood plasma is a 

 compound of the elements sodium (symbolized by the 

 letters Na), hydrogen (H), carbon (C) and oxygen (O) 

 in three parts (ordinary cooking soda). This compound 

 is known chemically as sodium bicarbonate (NaHCOs). 

 The symbol of carbonic acid, which results from dissolving 

 carbon dioxide (CO2) in water (HoO), is H2C0i. Now the 



