RESPIRATION AND ACIDOSIS 309 



The reaction of blood serum is about Pn7-35- The maximum varia- 

 tions are P H 7 to P H 8. The former value (i.e., neutrality) may be 

 reached in very severe acidosis whereas the maximum alkaline value of 

 P H 8 may be reached by alkali administration. The average value for 

 normal urine is P H 6 and for gastric juice P H i.77. 



Even under normal conditions the human body is continually 

 forming acids as a result of oxidations taking place in intermediary 

 metabolic changes. For example, the sulphur of the proteins we eat 

 is oxidized to sulphuric acid, whereas, carbonic acid results from the 

 transformation not only of proteins but of fats and carbohydrates as 

 well. Moreover, there are small amounts of various organic acids 

 produced and ultimately oxidized with the formation of carbon dioxide 

 and water, although a certain quantity of some of these acids, notably 

 lactic and uric, is excreted as such. 



Let us examine into the factors which the blood calls to its aid 

 in maintaining its accustomed reaction in the* face of normal or ab- 

 normal acid production. In this connection we must consider (i ) sodium 

 bicarbonate and carbon dioxide which are present in proper quantity 

 to yield a nearly neutral reaction, (2) the acid monosodium hydrogen 

 phosphate and the alkaline disodium hydrogen -phosphate which also 

 are present in proper proportion to yield a similar nearly neutral re- 

 action as that formed by the sodium bicarbonate and carbon dioxide, 

 (3) the proteins which are amphoteric and, therefore, combine with acids 

 or alkalies without change in reaction. The carbonates of the blood are 

 of prime importance in maintaining the constancy of reaction and have 

 been termed the "first line of defense." Carbon dioxide is being con- 

 stantly formed in the tissues. This is carried by the blood to the 

 lungs and eliminated in respiration as carbon, dioxide. Every 24 hours 

 an average adult eliminates in this way acid equivalent to several 

 hundred cubic centimeters of concentrated hydrochloric acid. Owing 

 to the operation of laws which govern the reaction of solutions of weak 

 acids and the salts of such acids, the blood is able to take up a quantity 

 of the acid carbon dioxide without undergoing any appreciable change 

 in reaction. In this way large amounts of acid are daily eliminated 

 from the body, and the mechanism is so nicely adjusted that the 

 organism is subjected to no strain of any sort. 



If we could hold our breath for a sufficiently long time while the 

 circulation continued normally we would finally reach a point where 

 the carbon dioxide concentration would be the same in the alveolar 

 air as in the blood and tissues. The process of respiration lowers the 

 concentration of carbon dioxide in the lungs. This in turn permits the 

 entrance of carbon dioxide from the blood into the alveoli of the lungs 



