76 LABORATORY WORK IX PHYSIOLOGICAL CHEMISTRY. 



of the oxygen combination renders the compound particularly 

 liable to the action of reducing agents. A reduction of this 

 kind takes place in the capillaries of the tissues, hemoglobin 

 or reduced hemoglobin being formed, the presence of which 

 in predominating quantities gives to the venous blood its 

 characteristic dark red color. 



Hemoglobin is very prone to combine to form derivatives 

 with certain compounds such as carbon monoxide, nitric 

 oxide, and hydrogen sulphide. These simple substances, 

 having a greater affinity for the hemoglobin molecule than 

 the oxygen possesses, replace the latter readily and form 

 stable and more or less toxic compounds which cause death 

 by oxygen starvation. Again, partial decomposition prod- 

 ucts of hemoglobin showing characteristic spectra are easily 

 formed under certain conditions; such are methemoglobin, 

 hemochromogen, hematoporphyrin, etc. Some slight phys- 

 ical and chemical differences seem to exist between the oxy- 

 hemoglobins obtained from the blood of various animals, a 

 fact which explains why the coloring matter from the blood 

 of different animals does not crystallize in the same form or 

 with the same facility. 



Place on a glass slide one drop of defibrinated dog's blood. 

 To this add one drop of water and mix with a platinum wire. 

 Allow the mixture to evaporate at room temperature until the 

 edges of the drop have begun to dry. Then place a cover- 

 glass on the slide and examine under the microscope. Sketch 

 the crystals of oxyhemoglobin. 



The proof for the presence of oxyhemoglobin is usually 

 adduced by showing under the microscope crystals of hemin. 



Hcemin Teichmann's Crystals. 

 Hemin is the HC1 ester of the anhydride of hematin. 

 Place one drop of NaCl solution upon a microscopic slide 



