426 BLOOD AND LYMPH. 



becomes exposed more or less completely to the action of the air, 

 and the utilization of the entire quantity of hemoglobin must be 

 nearly perfect. Instruments known as hemometers or hemo- 

 globinometers have been devised for clinical use in determining 

 the amount of hemoglobin in the blood of patients. A number of 

 different forms of this instrument are in use. In all of them, how- 

 ever, the determination is made with a drop or two of blood, such 

 as can be obtained without difficulty by pricking the skin. The 

 amount of hemoglobin in the withdrawn blood is determined 

 usually by a colorimetric method — that is, its color, which is due 

 to the hemoglobin, is compared with a series of standard solutions 

 containing known amounts of hemoglobin, or with a wedge of 

 colored glass or a solution whose color value in terms of hemo- 

 globin has been determined beforehand. For details of the struc- 

 ture of the several instruments employed and the precautions to 

 be ol^served in their use reference must be made to the laboratory 

 guides. * 



Compounds with Oxygen and Other Gases. — Hemoglobin has 

 the property of uniting with oxygen gas in certain definite propor- 

 tions, forming a true chemical compound. This compound is known 

 as oxyhemoglobin; it is formed whenever blood or hemoglobin solu- 

 tions are exposed to air or are otherwise brought into contact with 

 oxygen. According to a determination by Hiifner,t one gram of 

 hemoglobin combines with 1.36 c.c. of oxygen. These figures 

 would indicate the probability that each molecule of hemoglobin 

 unites with a molecule of oxygen, since 1.36 c.c. of oxygen weighs 

 approximately 0.0019 + gram, and the ratio of 1 gram of hemoglobin 

 to 0.0019 gram of oxygen is that of the molecular weight of hemo- 

 globin to the molecular weight of oxygen, that is, 16669:32 : : 

 1: 0.0019. It should be stated that some observers J find that the 

 maximum oxygen capacity of the blood may show individual varia- 

 tions within narrow limits, and that, therefore, what we designate as 

 hemoglobin may not be a single chemical substance, but a mixture 

 of closely related compounds. Oxyhemoglobin is not a very firm 

 compound. If placed in an atmosphere containing no oxygen 

 it is dissociated, giving off free oxygen and leaving behind hemo- 

 globin or, as it is often called by way of distinction, "reduced 

 hemoglobin.'" This power of combining with oxygen to form a 

 loose chemical compound, which in turn can be dissociated easily 

 when the oxygen pressure is lowered, makes possible the function 

 of hemoglobin in the blood as the carrier of oxygen from the lungs 

 to the tissues. The details of this process are described in the 



* See Simon, "A Manual of Clinical Diagnosis," Philadelphia. 



t "Archiv. f. Physiologie," 1894, p. 130. 



i See Bohr, in Nagel's "Handbuch der Physiologie," vol. i, pt. 1, 1905. 



