24 8 TEXT-BOOK OF PHYSIOLOGY 



wound in the finger or elsewhere and then dropped into the tube B, in which 

 a small quantity of distilled water from E was previously placed to prevent 

 coagulation. The cap of G is then attached to a gas burner, through which 

 flows either pure CO or a gas containing CO and the rubber tube inserted 

 into D to the level of the water. After the gas has been flowing for a few 

 seconds the rubber tube is withdrawn, and while the glass tube is yet full of 

 the gas, it is closed with the thumb and gently shaken so as to convert all the 

 hemoglobin into carbon-monoxid hemoglobin. This is then diluted very 

 gradually as in the employment of the Gowers apparatus until the tint of 

 the solution in B corresponds to that in A. The level at which this is 

 observed indicates the percentage of hemoglobin in the blood used. The 

 error in this method scarcely exceeds i per cent. 



Von Fleischl's hemometer consists of a metallic cell divided into two 

 compartments, a and a', by a vertical partition (Fig. 100). In the former 

 a definite quantity of blood is placed and diluted with a known quantity of 

 water. Beneath the compartment a' is placed a glass wedge stained with 

 the golden purple of Cassius or similar pigment, the color of which passes 

 from a deep red at one end to clear glass at the other (Fig. 101). To the 



side of this wedge is placed a scale 

 ranging from o to 120. By means of 

 the screw, R T, the glass wedge is 

 moved until the color of the glass and 

 diluted blood is identical. The illum- 

 ination of the blood and glass wedge is 

 FIG. IOI.-TINTED GLASS WEDGE OF THE accomplished by lamp-light reflected 

 VON FLEISCHL HEMOMETER. from the white reflecting surface 



beneath. The depth of color of the 



glass opposite 100 on the scale corresponds to that of normal blood. If, 

 therefore, the colors are identical at 75 divisions, the blood contains but 75 

 per cent, of the normal amount of hemoglobin. 



Absorption Spectra. Both oxyhemoglobin and reduced hemoglobin, 

 like other soluble pigments, have an absorbing influence on certain waves 

 of light, and hence give rise to absorption bands which can be studied 

 with the spectroscope, and which are so characteristic as to serve for their 

 identification. 



In principle a spectroscope consists of a prism which decomposes the 

 light from a narrow slit into a band of all the spectral colors. A form of 

 spectroscope in common use is that shown in Fig. 102. It consists of a 

 tube, B, which has at one end a slit that can be narrowed or widened by 

 means of a screw. The light, having passed through it, falls on an achro- 

 matic convex lens (called the collimator) at the opposite end of the tube 

 which renders the divergent rays of light parallel. These parallel rays sub- 

 sequently fall on the prism, by which they are dispersed and directed into the 

 tube, A, which is nothing more than a small telescope. On looking into it 

 at the ocular end the spectral colors are seen. If the light has been derived 

 from the sun the spectrum will present vertical dark lines, the so-called 

 Fraunhofer s lines. They are given from A to F in Fig. 103. If a colored 

 medium be held in front of the slit so that the light has to pass through it first, 

 certain dark bands will appear in the spectrum, owing to the absorption of 

 certain rays. 



