76 THE CIRCULATING LIQUIDS OF THE BODY 



some of the alkali haematin is changed into haemochromogen by re- 

 ducing substances formed by the action of the alkali on the blood. 



(g) H&mochromogen. To a solution of alkaline haematin add a drop 

 or two of ammonium sulphide. The band near D disappears, and two 

 bands make their appearance in the green (Fig. 13, p. 51). 



(h) Hcsmatoporphyrin. Put some strong sulphuric acid into a test- 

 tube. Add a few drops of blood, agitate the test-tube till the blood 

 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. 13). 



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

 hospitals, and, indeed, a delicate one, but quite untrustworthy 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 or greenish-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, oxydases or 

 oxidizing ferments present, not only in the formed elements of blood, 

 but elsewhere, e.g., in fresh vegetable protoplasm, milk, seminal fluid, 

 and pus, will cause the same colour (p. 267), but not if they have been 

 previously boiled.* The test has been considered chiefly of value as 

 a negative test. When the blue colour is not obtained, we have good 

 evidence that, blood is absent. But, according to Buckmaster, if the 

 precaution of first boiling the liquid suspected to contain blood be 

 adopted, it is also a good positive test. It is, however, far inferior to 

 the haemin test (p. 78) where that can be obtained, and of course in- 

 ferior to the identification of erythrocytes with the microscope, or to 

 the spectroscopic identification of the blood-pigment where the material 

 is suitable for this. 



(4) Quantitative Estimation of Haemoglobin (a) By Haldane's Modi- 

 fication of Gowers' Hcemoglobinometer. Place in the graduated tube B 

 (Fig. 22) an amount of water less than will ultimately be required to 

 dilute the blood to the required tint. Puncture the finger or lobe of 

 the ear with one of the small lancets in F, and fill the capillary pipette D 

 to a little beyond the mark 20. Wipe the point of the pipette and dab 

 it on a piece of filter-paper till the blood stands exactly at the mark. 

 Blow the blood into the water in B, and rinse the pipette with the water. 

 Attach the cap of tube G to a gas-burner. Introduce the rubber tube 

 into B nearly to the level of the water, and allow gas to pass for a few 

 seconds . Withdraw the tube while the gas is still passing. Immediately 

 close the end of B with the finger, and move the tube so that the 

 liquid passes from end to end of it at least a dozen times, to saturate 

 the haemoglobin with carbonic oxide. While this is being done, the 

 tube should be held in a cloth, otherwise it will become heated, and 

 liquid will spurt out when the finger is removed. Water is now added 



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

 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 oxidizes 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 peroxi- 

 dase) 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), 



