PROTEINS 249 



some of the guaiacum solution. Observe the color. Repeat with 

 boiled carrot. The color does not form. The reaction also is 

 given by milk, pus, saliva, and various other substances, but 

 these substances do not give the test after having been boiled, 

 thus differing from blood. They contain an oxidase which is re- 

 sponsible for the reaction and which is destroyed by boiling. In 

 the case of blood, the reaction depends probably on the catalytic 

 action of the iron constituent of hematin. 



(d) Catalase. The presence of a catalase in blood may be dem- 

 onstrated readily. To a little defibrinated" blood add hydrogen 

 peroxide. Observe the bubbles of oxygen given off. This reac- 

 tion is due also in some measure to the blood pigment, but fresh 

 blood contains a catalase in addition. Repeat the experiment 

 with boiled blood. The test is negative, as the catalase is de- 

 stroyed by boiling. 



(e) (1) In testing a blood stain, in addition to the tests given 

 above, (a, b and c) a small portion of the fabric should be ex- 

 tracted with glycerol or 0.9% sodium chloride, and the extract 

 examined with the microscope for corpuscles. 



(2) An aqueous extract of the stain may be tested for the 

 formation of hemochromogen. If the stain does not dissolve in 

 water it may be extracted with acidified alcohol, and the extract 

 examined with the spectroscope for acid hematin. 



(f) The identification of a stain as human blood is accom- 

 plished by none of the above reactions. The final proof that a 

 blood stain has come from a human subject is obtained by agglu- 

 tination and hemolysis tests. 



iv. The globin constituent of hemoglobin may be demon- 

 strated as follows : Corpuscles are washed 2 or 3 times with iso- 

 tonic salt solution, the corpuscles being separated from the 

 liquid each time by centrifuging. A small quantity of the 

 washed corpuscles is then placed in a test tube, a small amount of 

 alcohol and of hydrochloric acid added and the mixture heated 

 on the water bath. The liquid turns a dark brown color due to 

 the formation of acid hematin, and a precipitate forms which 



