340 PRACTICAL PHYSIOLOGY 



That haemoglobin contains iron can be shown by the following 

 experiment : 



EXPERIMENT X. Dissolve some dried blood by heating with 

 strong nitric acid. Evaporate nearly to dryness in a dish. Dissolve 

 in water and add potassium sulphocyanide solution. A blood-red 

 colour indicates the presence of iron. 



Crystals of haemoglobin. These are most easily obtained from such 

 animals as the rat or guinea-pig ; with more difficulty from man and 

 most other mammals. 



EXPERIMENT XL Mix a drop of rat's blood with a drop of water 

 upon a slide. After several minutes examine under the microscope for 

 haemoglobin crystals. 



Haemoglobin, as we have seen, is a compound protein consisting of 

 two parts, the iron containing portion "haematin" and the protein 

 portion "gkbin" Haematin has the formula C 32 H 82 N 4 O 4 Fe. It itself 

 does not crystallise, but a compound of haematin with hydrochloric 

 acid and some other body (acetic acid, or an alcohol according to the 

 method of preparation) called haemin can be obtained from haemo- 

 globin, which crystallises in chocolate-brown rhombic plates. This 

 forms one of the chemical tests for blood. 



EXPERIMENT XII. Preparation of Haemin Crystals. Place a drop of 

 blood upon a glass slide and warm until dry. Scrape loose the brown 

 residue, add a little glacial acetic acid, cover with a cover glass and 

 warm very gently until bubbles form. Remove from flame. If 

 necessary add a little more acid, and warm again till bubbles form. 

 Repeat the operation two or three times. When cold examine with 

 microscope for the dark-brown haemin crystals (Fig. 228). 



There is sufficient chloride in blood to give the test without the 

 addition of any sodium chloride. If, however, an old blood stain be 

 used, it is necessary to add a small crystal of sodium chloride in case 

 the chloride of the blood has been washed out. Bromide or iodide may 

 be used instead of chloride, yielding a haemin with a corresponding 

 change in composition. 



Another chemical test for blood depends upon the fact that the iron 

 containing portion of the haemoglobin will, in the presence of such 

 oxidising agents as hydrogen peroxide, or old " ozonised " turpentine, 

 convert a coloured body like tincture of guiac (red) to another 

 coloured derivative (blue). 



EXPERIMENT XIII. Boil some diluted blood. Add 2 drops of 

 tincture of guiac (or of an alcoholic solution of guaiconic acid), 

 then sufficient alcohol to dissolve the precipitate, and lastly a little 

 ozonic ether, ozonic alcohol, or old oil of turpentine. A blue colour 



