ACIDOSIS 65 



of non-volatile acid invasion by respiratory reduction of the free carbonic 

 acid. Whenever, either by increased rate of CO 2 production or by decom- 

 position of BHCO 3 by acid, the ratio BHCO 3 :H 2 CO 3 ratio is decreased, 

 the respiration is accelerated. JVIore rapid ventilation follows until the 

 H 2 CO 3 of the blood is so reduced that the normal pH is restored. The 

 respiratory response is so sensitive that Campbell, Douglas, Haldane, and 

 Hobson (1913) observed that an increase of only 1 mm. in CO 2 tension, 

 sufficient to change the blood pH by less than 0.01, accelerated the minute 

 volume of air breathed by 60 per cent. 



When retention of non-volatile acids occurs gradually, as in metabolic 

 disease, the respiratory compensation rather than the buffers is the first 

 observable defensive reaction of the body. The respiratory control, 

 unless deadened by narcotics or toxins, is so sensitive that the slightest 

 fall in pH causes a compensatory increase in respiration and restoration 

 of a normal pH. The usually observed occurrence in naturally occurring 

 acid retentions is therefore a gradual lowering of the blood bicarbonate, 

 with proportionately increasing minute volume of the respired air, the 

 blood pH remaining normal until the bicarbonate has fallen to *4 or even 

 % of the normal level. Only when the fall is so great the respiration 

 can no longer increase in proportion to it does the pll begin to drop, indi- 

 cating that the buffers other than bicarbonate are being called on as the 

 next defense to the body's neutrality. 



3. The Excretion of Acid by the Kidneys. When either the pH or 

 the alkali reserve of the blood has been lowered the normal response of the 

 kidneys is to excrete acid products at an increased rate and restore the 

 internal condition to normal. This is true even when the acids concerned 

 are so strong that they can not themselves be excreted as free acids in any 

 significant proportion. Such acids react in the body with excretable 

 buffers, chiefly the phosphates, by such reactions as B(BHPO 4 ) -f- HC1 = 

 H(BHP0 4 ) + BC1. The acid phosphate H(BHPO 4 ) formed by the 

 reaction is excreted as such in the urine, while the strong acid is excreted 

 as the salt (e.g., BC1) formed by the reaction with the buffer (Fitz, Als- 

 berg, and Henderson, 1907). 



The pH of the urine varies from 4.8 to 7.4 (Henderson and Palmer, 

 1912). Whenever, as is almost always the case, the urinary pH is below 

 7.4, the kidneys excrete products the retention of which in the blood would 

 tend to lower its pH below that point. Such acid products, so far as 

 quantitatively significant amounts are concerned, are necessarily buffers. 

 Strong acids, like HC1, can be present free in only infinitesimal amounts 

 even at the lowest urinary pH. Of the acid products excreted, the chief 



B(BHPO 4 ) 

 is normally acid phosphate. In the blood, at pH 7.4, the ratio 



_ti(.t>-tiJr(J 4 ) 



is 3.93, 80 per cent of the total buffer being in the form of the alkaline 



