The dissociation curve in man 225 



These curves all lie within the black area marked in Fig. 109, the 

 upper boundary of this area being Ryffel's curve and the lower 

 boundary that of Douglas, Haldane and Mathison. This area, there- 

 fore, represents the limits within which the curves of human beings 

 may be regarded as normal at the present time. 



Having determined the limits between which any single individual 

 may be regarded as possessing a normal dissociation curve and the 

 degree of variability which may be regarded as normal in any single 

 person, we may now proceed to discuss some special cases of variation 

 when the body is subjected to abnormal conditions. Before doing so, 

 however, it is necessary to explain the meaning of certain words used 

 to denote the changes which we are about to describe. 



If the curve of a particular person moves from its normal position 

 it may move in either one of two directions, i.e. it may be either 

 above or below the normal curve of that person. In other words, 

 at a given oxygen pressure the blood may take up either more or 

 less oxygen than it is wont to do. To express these facts Mr Harrison, 

 Fellow of Trinity College, Cambridge, at the instance of Dr Fletcher, 

 suggested the following nomenclature ; when the dissociation curve 

 is above its normal situation, i.e. when at a given pressure of oxygen 

 the blood takes up an abnormally great percentage of its total 

 possible load of oxygen, the curve is called "pleonectic*." When on 

 the other hand it takes up less than the usual percentage of oxygen 

 it is "meionectic" ; when it becomes saturated to the normal extent 

 under any specified conditions it is "mesectic." If the curve becomes 

 meionectic the value of K will diminish, if pleonectic it will increase, 

 as compared with the normal or mesectic value. There is one point 

 which must be made perfectly clear to the reader ; normal blood in 

 any individual must yield a mesectic curve but blood which yields 

 a mesectic curve need not necessarily be normal. Let me give a case 

 in point. In Chapter V it was shown that if carbonic acid were 

 withdrawn from blood, the value of K would increase, i.e. the curve 

 would rise ; if this happened in a person and nothing else, he would 

 acquire a pleonectic curve, but if at the same time that the CO. 2 was 

 withdrawn lactic acid was added to the blood the value of K would 

 diminish, and the curve would tend to return to its former position, 

 and if enough lactic acid were added the curve would become as it 

 was to start with. Again, if this process took place in a human being 



os-, disposed to take more than one's share. From 7rAeoi>et'a, a dis- 

 position to take more than one's share. (Liddell and Scott.) 



B. R. F. 15 



