504 RESPIRATION 



that practically all the oxygen is held by the corpuscles in the form of an unstable 

 chemical compound. 



It has been shown that the element which unites with the oxygen, 

 is the blood-pigment or hemoglobin of the red cells. This deduction 

 finds substantiation in the fact that oxygen is bound by crystalline 

 hemoglobin in quite the same way as by whole blood and in perfect 

 agreement with the law of the tension of the gases. Thus, if projected 

 upon an abscissa, the curve of absorption of oxygen by hemoglobin 

 forms a curved line, the convexity of which is turned upward. This 

 result proves that the absorption is greatest at low tensions and least 

 at high tensions, but the employment of hemoglobin, instead of whole 

 blood, introduces several factors which may render a direct comparison 

 of the results practically impossible. In the first place, it is difficult 

 to procure a solution of this pigment which can justly be compared 

 with samples of whole blood, and secondly, it is not always a simple 

 matter to exclude or to control the influence of the carbon dioxid up- 

 on the binding power of the hemoglobin. Thirdly, although oxygen 

 and hemoglobin form a dissociable compound, their dissociation ten- 

 sion may be varied by changes in temperature, as well as by the char- 

 acter of the salts present. Human blood corpuscles, for example, are 

 characterized by unusual amounts of potassium, whereas dog's cor- 

 puscles contain more sodium. The former salt is notably more effi- 

 cient in increasing the percentage of saturation of the hemoglobin than 

 the latter. In spite of these difficulties, however, the more recent 

 analyses have given a close quantitative agreement; for example, inas- 

 much as 1 g. of crystallized hemoglobin takes up about 1.3 c.c. of oxy- 

 gen, and inasmuch as whole blood absorbs about 20 volume per cent, of 

 this gas, the blood must contain about 15 per cent, of this pigment. 

 The correctness of this value has been established by analytical means; 

 moreover, the absorption of the oxygen may be ascertained directly 

 by determining the binding power of the iron of the blood. Inas- 

 much as this substance is normally held in measurable quantities 

 only in the hemoglobin, a direct comparison may be made between 

 the absorptive power of this pigment and its content in iron. It 

 seems, therefore, that the hemoglobin is present in amounts sufficient 

 to combine with practically all the oxygen ordinarily contained in the 

 blood. 



It has also been found that the oxygen may be displaced from the 

 hemoglobin by equivalent amounts of carbon monoxid and nitrous 

 oxid, and furthermore, may be made to absorb carbon dioxid in greater 

 quantities than can be accounted for by the laws of solution. This 

 fact seems to suggest that the hemoglobin is also capable of entering 

 into a loose chemical combination with this gas, although it does not 

 permit its oxygen to be directly displaced by it. Conditions may 

 arise, therefore, which lead to a simultaneous saturation of the hemo- 

 globin by oxygen and carbon dioxid, thereby altering the oxygen- 

 carrying capacity of this pigment. As has been stated above, it is the 



