134 



ELEMENTS OF /APPLIED MICROSCOPY. 



thus obtained, when placed in a cell, covered and ex- 

 amined with the low objective, shows the spectrum of 

 oxyhsemoglobin with dark bands in the yellow and 

 green, shown in Fig. 50 at 4. If a drop of ammonium 

 sulphide be added, the two bands will fuse into one, giving 



Fig. 50. — Spectra of Oxyhsemoglobin and reduced ILemoglobin. 

 (After Howell.) 



the spectrum of reduced haemoglobin, shown at B. 

 The addition of a little citric acid to a solution of oxy- 

 hsemoglobin produces the spectrum of acid haematin, 

 with a broad band in the red, a narrow one in the green, 

 and a very faint band in the blue. In old blood-stains 

 the oxyhsemoglobin has been changed to hsematin, and 

 since this substance is insoluble in water, no color- 

 ation of the liquid appears when the stain is treated as 

 above. In such a case a little acetic acid must be tried; 

 this dissolves hasmatin, and the solution at once pro- 

 duces the acid haematin spectrum. On adding am- 

 monia, the broad band in the red disappears. Blood- 

 stains in which the hsemoglobin is only partially changed 



