310 PHYSIOLOGICAL CHEMISTRY 



and the consequent lowering of the blood carbon dioxide permits the 

 entrance into the blood of carbon dioxide from the tissues where the 

 concentration of carbon dioxide is the highest. In acidosis the carbon 

 dioxide concentration of the alveolar air is lowered because of hyperpnea 

 and because of the fact that the power of the blood to carry carbon 

 dioxide has been lowered. 



When acids such as /3-hydroxy butyric, lactic and hydrochloric are 

 added to the blood they react with the sodium bicarbonate and disodium 

 phosphate forming a sodium salt which is neutral in reactiom, mono- 

 sodium phosphate which is slightly acid, and free carbonic acid. The 

 carbonic acid and acid phosphate ionize to but a small degree and 

 therefore the hydrogen ion concentration of the blood is but slightly 

 altered. We have here a very efficient factor in the regulation of 

 blood reaction following an influx of acid or alkali. The regulatory 

 mechanism is further aided by the rapid elimination of the acid phos- 

 phate and carbonic acid, the former by way of the urine and the latter 

 by way of the lungs in the form of carbon dioxide. The following 

 equations represent what takes place when an excess of acid (HC1) 

 enters the blood. 



kidneys lungs 



T t 



NaHCOs + HC1 -> NaCl + H 2 O + CO 2 



kidneys kidneys 



T T 



Na 2 HPO 4 + HC1 -* NaCl + NaH 2 PO 4 



The name "buffer substances" has been given to the sodium phos- 

 phate and sodium bicarbonate of the blood in view of their protective 

 r61e'in preventing pronounced changes in blood reaction after acid or 

 alkali introduction. If large amounts of acids are continually poured 

 into the blood these buffer substances decrease in amount and finally 

 when the body can no longer replace the destroyed buffers acidosis 

 results. In fact we may consider that acidosis is any condition in 

 which the buffer substances of the blood are reduced below normal. 

 Hence acidosis is "lowering of the alkali reserve" of the body. When 

 such a reduction occurs the capacity of the blood to transport acids is 

 lowered. We have seen that carbonic acid is the acid most abundantly 

 produced in the body hence the "buffer" depletion lowers the power 

 of the blood to carry this acid. In case this depletion is sufficiently 

 pronounced carbonic acid accumulates in the tissues. It is well known 

 that the respiratory center is very susceptible to acid stimulation such, 

 e.g., as that afforded by carbonic acid. Hence a more thorough ventila- 

 tion of lungs and blood results and the more rapid removal of oarbon 

 dioxide prevents its further accumulation in the tissues. This hyperpnea 

 resulting from a stimulated respiratory center is one of N the clinical 



