436 



THE BLOOD 



[en. xxvi. 



however, by reducing agents like ammonium sulphide, be made to 

 yield haemoglobin. Methsemoglobin is of a brownish -red colour, and 

 gives a characteristic absorption band in the red between the C and 



FIG. 369. The photographic spectrum of haemoglobin and oxyhsemoglobin. (Gamgee.) 



D lines (spectrum 7 in coloured plate). In dilute solutions other 

 bands can be seen. 



Potassium ferricyanide is the most convenient reagent for making methaemo- 

 globin. It is, however, necessary to mention that it produces another effect as 



HK LM N 



I 



FIG. 370. The photographic spectrum of oxy haemoglobin and methsemoglobin. (Gamgee.) 



well, namely, it causes an evolution of gas, if the blood has been previously laked 

 by the addition of an equal quantity of water. This gas is oxygen ; in fact/all the 



