62 DONALD D. VAN SLYKE 



that, in human blood at least, these two bases predominate in the two 

 locations, and do not diffuse freely from one to the other. There is, of 

 course, some K in the plasma, and some Na in the cells, which the above 

 diagram fails to show. 



The cell buffers, phosphates and alkali salts of hemoglobin, from their 

 location in the cell are able, when the plasma pH falls, to draw HC1 from 

 the plasma into the cells, where it is neutralized by Reactions 3, 4, and 5. 

 This withdrawal permits the increase of plasma BHCO 3 by Reaction 1. 

 The cells are also freely permeable to H 2 CO 3 , so that the latter can enter 

 them and be neutralized by Reactions 6, 7, and 8. The cells can therefore, 

 if acid enters the plasma, use their buffers both to increase the BHCO 3 

 and lower the H^COg in the plasma, and thereby lessen the fall in 

 plasma pH. 



Concerning the relative parts which the different reactions in the 

 diagram play, our knowledge is not exact. It appears, however, that a 

 given change in H 2 CO 3 causes the same change in BHCO 3 in the cells 

 that it does in the plasma. That is, the BHCO 3 formed by Reactions 1 

 and 2 in the plasma equals that formed by Reactions 6, 7, and 8 in the 

 cells. This is exemplified by the data of Van Slyke and Cullen (1917) 

 and Joffe and Poulton (1920). 



Furthermore it is known that from 50 to 75 per cent of the BHCO 3 

 formed in the plasma by a given increase in H 2 CO 3 results from Reaction 

 1 and the accompanying shift of HC1 into the cells. 



A result of the latter fact is that the BHCO 3 of separated plasma is 

 dependent on the H 2 CO 3 concentration of the whole blood at the moment 

 the plasma is separated. Consequently, if the blood is allowed to lose or 

 absorb CO 2 , after it has left the body and before the plasma is separated 

 from the cells, gross changes occur in the plasma bicarbonate, so that the 

 latter ceases to represent at all the conditions of the blood when it was 

 drawn. For example, if freshly drawn blood is poured back and forth 

 from one tube to another for a few minutes, half the total CO 2 may be 

 lost and all the reactions represented in the diagram move from right to 

 left, with the result that the plasma when subsequently separated may have 

 only about half as much BHCO 3 as when it was drawn from the body. 

 Subsequent restoration of the original H 2 CO 3 to the separated plasma 

 restores only about !/4 of the BHCO 3 , since because of absence of the 

 cells Reaction 1 can no longer to reversed, and only the small amount of 

 BHCO 3 formed by reversing Reaction 2 can be restored. For studies of 

 the acid-base balance on the plasma, the latter must be separated before 

 there has been any escape of CO 2 from the whole blood. 



c. The Interchange of Buffer Effects Between the Blood and the Tis- 

 sues. The buffers of the tissues are, like those of the blood cells, and prob- 

 ably by a similar exchange mechanism, available to assist in maintaining 

 neutrality of the blood plasma. The tissue buffers thus multiply several 



