GENERAL PROPERTIES! THE CORPUSCLES. 403 



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 The amount of hemoglobin in the withdrawn 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 

 observed 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 

 solutions are exposed to air or otherwise brought into contact with 

 oxygen. Each molecule of hemoglobin is supposed to combine with 

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

 the O capacity of the Hb of ox's blood is 1.34 c.c. to each gram of 

 Hb. It should be stated that some observers I find that the maxi- 

 mum oxygen capacity of the blood may show individual variations 

 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 

 as carbon monoxid hemoglobin. In this compound also the union 

 takes place in the proportion of one molecule of hemoglobin to one 

 molecule of the gas. The compound formed differs, however, 

 from oxyhemoglobin in being much more stable, and it is for this 

 reason that the breathing of carbon monoxid gas is liable to prove 

 fatal. The CO unites with the hemoglobin, forming a firm com- 



* See Simon, "A Manual of Clinical Diagnosis." Philadelphia, 1904. 



t 'Archiv f. Physiologic, " 1894, p. 130. 



t See Bohr, in Nagel's "Handbuch der Physiologie," vol. I., pt. I., 1905. 



