432 



THE BLOOD. 



[CH. XXVI. 



If we now interpose between the source of light and the slit S 

 a piece of coloured glass (H in fig. 364), or a solution of a coloured 

 substance contained in a vessel w T ith parallel sides (the hsemato- 

 scope of Herrmann), the spectrum is found to be no longer 

 continuous, but is interrupted by a number of dark shadows, or 

 absorption bands corresponding to the light absorbed by the 

 coloured medium. Thus a solution of oxyhsemoglobin of a certain 

 strength gives two bands between the D and E lines; haemoglobin 

 gives only one ; and other red solutions, though to the naked eye 

 similar to oxyhsemoglobin, will give characteristic bands in other 

 positions. 



A convenient form of small spectroscope is the direct vision 



Fig. 364. Diagram of spectroscope. 



spectroscope, in which, by an arrangement of alternating prisms of 

 crown and flint glass, the spectrum is observed by the eye in the 

 same line as the tube furnished with the slit indeed slit and 

 prisms are both contained in the same tube. 



In the examination of the spectrum of small coloured objects 

 a combination of the microscope and direct vision spectroscope, 

 called the micro-spectroscope, is used. 



The next figure illustrates a method of representing absorption 

 spectra diagrammatically. The solution was examined in a layer 

 i centimetre thick. The base line has on it at the proper dis- 

 tances the chief Frauenhofer lines, and along the right-hand 

 edges are percentages of the amount of oxyhsemoglobin present 

 in I, of haemoglobin in II. The width of the shadings at each 

 level represents the position and amount of absorption corre- 

 sponding to the percentages. 



The characteristic spectrum of oxyhsemoglobin, as it actually 

 appears through the spectroscope, is seen in the accompanying 



