ELEMENTARY CHEMICAL PHYSIOLOGY 245 



or iodide may be used instead of chloride, yielding a hsemin 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 guaiac (brown) 

 to another coloured derivative (blue). 



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

 tincture of guaiac (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 is formed in the presence of blood. Ascertain in what 

 dilution blood gives this test. Ozonic ether and ozonic alcohol 

 contain hydrogen peroxide. 



The solution is first boiled to destroy any oxidising enzymes present. 

 These bodies can effect the same change, as also can many salts of metals, 

 such as copper, iron, gold, cobalt, strong sodium chloride solution, and various 

 other fluids such as milk, saliva, mucus, sweat, and juices of vegetable origin 

 (extract of pea flour, fruit juices, etc.). If, however, the solution be first 

 boiled, in the absence of metallic salts, the reaction is to be regarded as a 

 reliable one for blood. In any case, if the test be negative, most investigators 

 regard it as certain that blood is absent. 



Other bodies such as aloin, benzidin, the leuco-base of malachite green and 

 phenol -phthalin can take the place of guaiac (see Blood in faeces, p. 305). 



The function of haemoglobin is to carry oxygen to the tissues. 

 This power of taking up oxygen can easily be demonstrated by 

 shaking up venous blood with air (see under Spectroscope). The 

 oxygen carrying capacity of blood can be ascertained as follows : 



EXPERIMENT XIII. In the bottle of a Dupre apparatus (see 

 Fig. 257) take 20 c.c. of oxygenated blood and 30 c.c. dilute 

 ammonia solution (1 am. : 500 water). In the small tube take 5 c.c. 

 of fresh saturated potassium ferricyanide solution. Adjust the 

 water to the zero of the apparatus by means of the clip and then upset 

 the ferricyanide into the blood. Shake well. Readjust the level 

 of the water and read how much oxygen has been given off. 



CHAPTER XII 



THE SPECTROSCOPIC EXAMINATION OF HEMOGLOBIN 

 AND ITS DERIVATIVES 



A spectroscope consists essentially of a screen, in which there is 

 a small slit, through which light from any desired source can pass, 

 a prism, and a series of lenses forming the telescope, through which 

 the observer looks. 



For qualitative work the small direct vision spectroscope (Fig. 

 179) is serviceable. When the position of the bands, however, is 

 required, one of the larger compound forms is necessary. 



