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Methaemoglobin. Methaemoglobin is prepared chemically by 

 adding amyl nitrite to blood. It contains the same amount of oxy- 

 gen as haemoglobin, but, owing to its different combination, the 

 oxygen cannot be removed even in a vacuum; hence it cannot be a 

 transporter of oxygen to the tissues. Potassium chlorate and the 

 continued use of antipyrin and acetanilid will produce methaBmo- 

 globin. 



Carbon-monoxide Haemoglobin, or Carboxyhsemoglobin. With 

 carbon-monoxide gas (CO) haemoglobin forms a compound similar to 

 oxyhaemoglobin, but known as carbon-monoxide haemoglobin. This 

 union is much more stable than the preceding, so that when carbon- 

 monoxide gas is breathed in excess death results from asphyxia, since 

 the tissues are prevented from receiving their proper supply of 

 oxygen. 



Carbon-monoxide results from the incomplete combustion of 

 carbon in coal and charcoal stoves. Its poisonous properties are 

 caused by its combining so firmly with the haemoglobin of the cor- 

 puscles that it prevents union with oxygen, and so produces asphyxia. 

 The blood of both veins and arteries is bright, cherry-red in color. 

 In poisoning from this gas, artificial respiration with saline trans- 

 fusion is sometimes of avail. 



For a better understanding of the import of the absorption 

 bands of the coloring matters in the blood, a brief description will 

 be given of the instrument whereby they are studied. 



THE SPECTROSCOPE. 



When white light, or that which reaches us from the sun, passes 

 from one medium into another more dense, it is decomposed into 

 several kinds of light, a phenomenon to which the name dispersion 

 is given. Thus, when a pencil of the sun's rays is passed through 

 a prism of flint glass, it is broken up into the seven colors of the 

 spectrum. This band of colors may be seen naturally in the form 

 mentioned as being placed inside the apparatus and is reflected up 

 through the slit belonging to the compound prism. If any incan- 

 descent object is placed in a suitable position with reference to the 

 aperture its spectrum will be obtained and will be seen on looking 

 through it. F shows the position of the field-lens of the eyepiece. 

 G is a tube made to fit the microscope to which the instrument is 

 applied. To use this instrument insert G like an eyepiece in the 

 microscope tube, taking care that the slit at the top of the eyepiece 

 is in the same direction as the slit below the prism. Screw on to 



