428 BLOOD AND LYMPH. 



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 

 hemoglobinometers 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, however, 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 The amount of hemoglobin in the withdrawn 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 whose color value in terms of hemo- 

 globin has been determined beforehand. For details of the structure 

 of the several instruments employed and the precautions to be ob- 

 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 

 section on Respiration. Hemoglobin forms with carbon monoxid 

 gas (CO) a compound, similar to oxyhemoglobin, which is known 



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



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



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



