VI.] THE COLOURED BLOOD CORPUSCLES. 49 



bands of oxy-haemoglohin are replaced by one absorption-band 

 between D and E, not so deeply shaded, and with its edges less 

 defined (fig. 24, 4). By shaking the solution very vigorously with 

 air, and looking at once, the two bands may be caused to re- 

 appear for a short time. Observe the absorption of the light 

 at the red and violet ends of the spectrum according to the 

 strength of the fluid. 



(c.) Dilute the solution, and observe that the single band is 

 not resolved into two bands, but gradually fades and disappears. 



((/.) To a similar solution of oxy-hsemoglobin, showing two 

 well-defined bands, add Stokes's fluid, and observe the single 

 absorption-band of haemoglobin. Shake the mixture with air and 

 the two bands reappear. 



(e.) Use a solution of oxy-haemoglobin where the two bands can 

 just he seen, and .reduce it with either ammonium sulpliide or 

 Stokes's fluid, and note that, perhaps, no absorption-band of hasmo- 

 globin is to be seen, or only the faintest shadow of one. 



(/.) Compare the relative strengths of the solution of oxy- 

 h£emoglobin and hsemoglobin. The latter must be considerably 

 stronger to give its characteristic spectrum. 



Fig. 25 shows the amount of light absorbed by solutions of 

 reduced haemoglobin (i cm. in thickness), and of various strengths. 



Stokes's Fluid. — Make a solution of ferrous sulphate ; to it add 

 ammonia after the previous addition of sufficient tartaric acid to 

 prevent precipitation. Add about three parts by weight of tartaric 

 acid to two of the iron salt. Afake it fresh when required. 



8. Reduction of HbOg by Putrefying Bodies.— Fill a test-tube with a dilute 

 solution of oxy-hsemoglobin or blood, add a drop of putrid meat infusion, cork 

 the vessel tightly to make it air-tight, and allow it to stand. I'he oxy-hoemo- 

 globin is reduced to hremoglobin, the colour changes to i)urj)le-red, and the 

 Huid shows the spectrum of h;vmoglobin. A better plan is to seal up the 

 blood in a tube. It need not be mixed with putrid matter in order to observe 

 after a time the reduction. 



9. Haematinometer. — For accurate observation, instead of a test-tube the 

 blood is introduced into a vessel with parallel sides, the glass plates being 

 exactly i cm. apart (fig. 31 D). Study this instrument. 



10. Hgematoscope (fig. 27). — By means of this instrum.ent the depth of the 

 stratum of fluid to be investigated can be varied, and the variation of the 

 spectrum, with the strength of the solution, or the thickness of the stratum 

 through which the light passes, at once determined. Study this instrument. 



11. III. Carbonic Oxide-Hsemoglobin. — Through a diluted solu- 

 tion of oxy-haemoglobin or defibrinated blood pass a stream of car- 

 bonic oxide — or coal gas — until no more CO is absorbed. Note the 

 florid cherry-red colour of the blood. 



D 



