ANIMAL FLUIDS AND TISSUES. 659 



diffused and poorly defined band, as though two oxyhsemoglobin bands had 

 gone together and had been displaced to the left (Fig. 72, 6). When the solu- 

 tion is agitated with air its color changes to bright red and the spectrum again 

 shows oxy haemoglobin. 



c. Methcemoglobin. To a dilute solution of blood add a drop or two of a 

 freshly prepared 10 per cent, solution of potassium ferricyanide. The color of 

 the solution becomes brown. Add just enough sulphuric acid to give a slightly 

 acid reaction and examine spectroscopically, when the spectrum is seen repre- 

 sented in Fig. 72, c. On rendering the solution slightly alkaline and adding 

 a few drops of Stokes' fluid the methaenioglobin changes to haemoglobin, and 

 on agitating with air into oxyhsemoglobin. These changes can easily be fol- 

 lowed with the spectroscope. 



d. Add hcematin. To a few drops of undiluted blood add a drop or two of 

 acetic acid. The haemoglobin is broken up into a histon called globin, and a 

 non-protein substance called hsemin. The solution which results is almost 

 black, but on diluting with water is seen to be red. The spectrum has a band 

 in the red, almost coincident with the band shown by methsemoglobin in 

 neutral or acid solution. 



e. Alkaline hcematin. To a portion of acid hsematin solution add sodium 

 hydroxide until the precipitate which forms has redissolved. The solution 

 will be alkaline and, if properly diluted, will show a poorly defined band to 

 the left of the D line. It is usually observed, however, that the entire spec- 

 trum is absorbed except the red. (Fig. 72, d.) 



f. Reduced hcematin (Hsemochromogen). Reduce a portion of alkaline 

 haematm solution with Stokes' fluid, and after properly diluting examine 

 Bpectroscopically. Two sharply defined dark bands are seen between D 

 and E, which seem to be coincident with the bands produced by oxyhaemoglo- 

 bin. It will be- noted, however, that the light which emerges on the left of the 

 left band is plainly green. By diluting the solution with water the band on 

 the right may be made to disappear, while the other band is still very dark. 

 (Fig. 72, e .) 



g. Hcematoporphyrin. Add a drop of blood to a few c.c. of concentrated 

 sulphuric acid, mix well, dilute with water, and render alkaline with sodium 

 carbonate. The spectroscope shows four bands. (Fig. 72, /.) 



h. Carbon monoxide hcemoglobi?i. Pass a slow current of carbon monoxide 

 (illuminating-gas, containing carbon monoxide, may be used) through 50 c.c. 

 of blood until its color is bright red. Examined spectroscopically, the bands 

 seen occupy nearly the same position as those of oxy haemoglobin, but they do 

 not disappear on treatment of the solution with Stokes' fluid. (Fig. 72. g.) 



On adding to 10 c.c. of carbon monoxide haemoglobin solution 15 c.c. of a 

 20 per cent, solution of potassium ferrocyanide the mixture shows a bright-red 

 color. On treating oxyhsemoglobin solution in the same way, it assumes a 

 grayish-brown or green color. 



Examination of blood-stains. Blood-stains may be recognized, 

 after having been washed off with as little water as possible, by the 

 following methods : 



1. Examine the reddish fluid under the microscope for blood cor- 

 puscles. 



