CHAP. IV.] THE BLOOD. METHODS OF RESEARCH. 219 



of the watch-glass, and the liquid is evaporated to dryness. The 

 watch-glass is then examined with a magnifying power of about 

 350 diameters. If no crystals are perceptible, more acetic acid 

 may be added and the process of boiling and evaporation repeated. 

 If present, the crystals present the appearance shewn in Fig. 24 (page 

 115). 



Medico-Legal Detection of Carbonic Oxide in Blood. 



As was mentioned at page 105, carbonic oxide expels the oxygen 

 from oxy-haemoglobin and forms a more stable compound, which is 

 not affected by the alkaline reducing solutions which readily reduce 

 oxy-haemoglobin. Blood of animals poisoned with carbonic oxide, if 

 nearly saturated with the gas, presents a remarkably persistent 

 vermilion colouration ; if not saturated, the colour may not be very 

 distinctly affected. 



The action of a solution of caustic soda of specific gravity 1*3 

 establishes a very remarkable difference between CO-blood and 

 normal blood 1 . This reagent when added to normal blood converts it 

 into a black, slimy, mass, which when spread in thin layers over a 

 porcelain capsule appears of a greenish brown colour; blood which 

 has absorbed carbonic oxide presents, on the contrary, after treatment 

 with its own volume of the solution of caustic soda, the appearance of 

 a firmly coagulated mass, and, when spread on porcelain, appears of a 

 cinnabar-red colour. 



It has been recommended that, instead of employing a simple 

 solution of caustic soda, a mixture of two parts of a solution of caustic 

 soda of sp. gr. T3, and 2J parts of a solution of chloride of calcium in 

 water (1 to 3), should be rubbed up with the blood in a porcelain 

 capsule, fifteen or twenty drops being sufficient for the reaction 2 . 



A more conclusive proof of the presence of carbonic oxide is 

 obtained with the aid of the spectroscope. The suspected blood is 

 suitably diluted so as to exhibit with perfect distinctness the two 

 absorption bands of O 2 -Hb or CO-Hb. Then a small quantity of 

 Stokes's reagent (ammoniacal solution of ferrous tartrate or citrate) is 

 added. In the event of the blood containing carbonic oxide the two 

 bands will not wholly fade, but will persist more or less distinctly. 

 When the blood is saturated with carbonic oxide the spectrum 

 undergoes no perceptible change under the influence of the reducing 

 solution. 



1 Hoppe, Virchow's Archiv, Vol. xi. Heft 3 (1857), p. 288. 



2 Eulenberg, Die Lehre von den schadlichen und giftigen Gasen. Braunschweig, 

 1865, p. 48. 



