134 ELEMENTS OF APPLIED MICROSCOPY. 
thus obtained, when placed in a cell, covered and ex- 
amined with the low objective, shows the spectrum of 
oxyhemoglobin with dark bands in the yellow and 
green, shown in Fig. so at A. If a drop of ammonium 
sulphide be added, the two bands will fuse into one, giving 
70 8665 do 55 §0 45 
! 
. 
; | 
3 D F ) 
70 =65 50 45 
B 
|! 
Fic. 50.—SPECTRA OF OXYHEMOGLOBIN AND REDUCED H&MOGLOBIN. 
(After Howell.) 
the spectrum of reduced hemoglobin, shown at B. 
The addition of a little citric acid to a solution of oxy- 
hemoglobin produces the spectrum of acid hematin, 
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 oxyhemoglobin has been changed to hematin, 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 hematin, and the solution at once pro- 
duces the acid hematin spectrum. On adding am- 
monia, the broad band in the red disappears. Blood- 
stains in which the hemoglobin is only partially changed 
