TRANSPORT OF OXYGEN 101 



high to a place of low oxygen tension is superior to that 

 of pure haemoglobin. 



This difference is due to the electrolytes, as is shown 

 by the follo\ving facts — 



1. If to haemoglobin, salts are added, the dissociation 

 curve approaches that of blood in the measure that the 

 amount of salts present approaches that which obtains in 

 blood. 



2. The form of the dissociation curve of blood varies 

 sHghtly, as does the saline content, in animals of different 

 species. If to the hajmoglobin of an animal A are added 

 salts as they occur in an animal B of another species, the 

 curve obtained corresponds with the blood of B. Therefore 

 the differences in the curves found in different species are 

 due to differences not in the haemoglobin, but in the sahne 

 constituents. 



The salts are beheved to exert their influence by causing 

 a clumping together of the haemoglobin molecules. 



B. The Reaction of the Blood. — That the curve is 

 materially affected by the degree of acidity of the blood 

 is shown in Fig. 22, which gives the effect of varying 

 amounts of COg. Acidity increases the tendency to 

 dissociation, the greatest effect being at an oxygen tension 

 of 20 mm. At tensions of 80 mm. and over the difference is 

 but shght. All acids have the same effect, the degree of 

 their influence varying with the extent to which they form 

 free hydrogen ions in blood. 



C. Temperature. — The effect of temperature is shown in 

 Fig. 22. With rise of temperature goes increased dis- 

 sociation, an increase which is greatest at low oxygen 

 tension. 



We therefore see first that the combination of haemoglobin 

 with oxygen is of such a nature that it is readily influenced 

 by three factors : the presence of salts, hydrogen ion con- 

 centration and temperature. We see, secondly, that these 

 factors exert their greatest influence at low tensions of 

 oxygen. We know, too, that of the three factors favouring 



