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A MANUAL OF PHYSIOLOGY 



dissolves, and examine the purple liquid, diluting it, if necessary, 

 with sulphuric acid. Its spectrum shows two well-marked bands, 

 one just to the left of D, and the other midway between D and E 

 (Fig. 7)- 



(3) Guaiacum Test for Blood. A test for blood much used in 

 hospitals, and, indeed, a delicate one, but not always trustworthy 

 unless certain precautions be taken is the guaiacum test. A drop 

 of freshly-prepared tincture of guaiacum is added to the liquid to 

 be tested, and then peroxide of hydrogen. If blood be present, the 

 guaiacum strikes a blue colour. The decomposition of the peroxide 

 by the blood is due mainly to the haemoglobin of the corpuscles. 

 Any derivative of haemoglobin which still contains the iron will act. 

 and boiling does not abolish this power. On the other hand, oxy- 

 dases or oxidizing ferments present not only in the formed elements 



FIG. 17. HALDANE'S MODIFICATION OF GOWERS' H/EMOGLOBINOMETER. 



of blood but elsewhere, e.g., in fresh vegetable protoplasm, 

 milk, seminal fluid, and pus, will cause the same colour (p. 264), 

 but not if they have been previously boiled.* The test has been 



* The formed elements of blood really contain no less than three fer- 

 ments of interest in this connection : (i) A catalase which decomposes 

 peroxide of hydrogen into water and molecular oxygen (i.e., oxygen not 

 in the atomic or nascent state). This reaction is given by both blood 

 and pus. (2) An oxydase (also spelled oxidase), which oxidises guaiacum 

 and similar substances without the presence of hydrogen peroxide. This 

 reaction is obtainable even from aqueous extracts of leucocytes. (3) A 

 peroxydase (also spelled peroxidase) which causes the oxidation of these 

 substances only in the presence of hydrogen peroxide, a reaction also 

 given by leucocytes. These ferments are all inactivated by .boiling 

 (Kastle). 



