174 RESPIRATION 



measure of the blood alkalinity. Even a strong solution of sodium 

 bicarbonate is but feebly alkaline ; but the amount of acid which 

 must be added to it to render it neutral is as great as if the sodium 

 were present as caustic soda, and is thus no measure of the actual 

 alkalinity of the solution. The carbonic acid united with the soda 

 prevents it from being at all strongly alkaline, but at the same time 

 does not completely neutralize it, and all weak acids have the same 

 properties. They may thus be said to be "buffer" substances, since 

 they prevent a strong acid from neutralizing at once a weakly 

 alkaline solution. A great deal of the strong acid has to be added 

 before the weak alkalinity is neutralized. The same applies to weak 

 alkalies, mutatis mutandis. 



Now the blood and tissues are full of buffer substances. In the 

 first place, as already seen in Chapter V, carbonic acid is present 

 in combination. Haemoglobin and various other proteins are also 

 present ; and it has been well known for a long time that proteins 

 act as both acid and alkaline buffers, so that the neutral point in a 

 solution containing proteins is very difficult to ascertain sharply 

 by means of ordinary indicators. The color alters gradually in 

 either direction as the neutral point for any particular indicator 

 is approached. It was shown in Chapter V that in the alkaline 

 blood haemoglobin and other proteins act as weak acids more than 

 sufficient in amount to combine with the bases not already com- 

 bined with strong acids, and that the presence of these proteins 

 along with carbonic acid determines the manner in which the 

 alkali in blood takes up and gives off CO 2 with varying partial 

 pressures of this gas. The amount of acid required to produce 

 neutrality is thus in itself no measure of the degree of alkalinity 

 in blood, but depends on the amount of the various buffer sub- 

 stances, including carbonic acid in combination with alkali ; and 

 they may vary considerably in amount under different conditions. 

 This has been pointed out very clearly by L. J. Henderson. 6 



It may be desirable at this point to remind the reader as to the 

 conception of acidity and alkalinity to which chemical and physi- 

 co-chemical investigation has led during the last thirty years. The 

 phenomena of electrolysis revealed to Faraday the fact that the 

 constituents of any "electrolyte," such as copper sulphate, are 

 torn asunder during electrolysis into definite fragments, of which 

 one kind travels toward the anode, and the other to the cathode. 

 These fragments he called "ions," because it is their movement 

 towards either anode or cathode, and the fact that each of them has 



" L. J. Henderson, Ergebn. der Physiol., VIII, p. 254, 1909. 



