IV 



THE BLOOD: FOKMED CONSTITUENTS 111 



the absorption ratio be represented by A, the coefficient of extinction by E, 

 and the content of colouring matter in 1 c.c. (calculated in grams) by C, it 

 follows tliat C will be equal to A x E. 



The most exact of the various instruments constructed for the determination 

 of coefficients of extinction is that of Kriiss. This (as shown by Fig. 36) 

 resembles an ordinary spectroscope, and differs from the spectro-photometers 

 of Vierordt, Hiifner and others, in that the two slits//' (Fig. 38) which give 

 the two spectra, one above the other, enlarge and contract in both directions 

 with a single movement of the screws V and V. 



To use this apparatus, fill a small pipette of capillary bore with blood to a 



FIG. 36. Spectro-photometer of Kriiss viewed as a whole. The extreme end of the eye-piece is 

 shown in Fig. 37. The extreme end of the objective is shown in detail in Fig. 38. The 

 lettering corresponds. The absorption-chamber containing the solution of the pigment to be 

 examined is shown in P"ig. 39. The third branch x, illuminated by a gas flame, projects the 

 millimetre scale on to the spectrum. 



given capacity, say 20 c. mm. This blood must be rapidly expelled into a 

 small beaker in which a measured quantity of distilled water has first been 

 placed, so that the blood is diluted in known measure. The degree of 

 dilution varies with the greater or less colouring power of the blood to be 

 tested, but as a rule the ratio of 1-200 is preferred. The pipette which held 

 the blood should be washed out several times with the water used for dilution, 

 and the liquid must be agitated till it is homogeneous in colour. The 

 absorption chamber (Fig. 39), which is a crystal cell with parallel faces, is 

 then filled, and a cube of glass, D, of the exact diameter of 1 cm., introduced, 

 to which the name of Schultz' cube is given. The two absorption spectra 

 are those of two strata of the same fluid differing by 1 cm. in depth. 



The extinction coefficients for human oxyhaemoglobin have been deter- 

 mined in two different regions of the spectrum, i.e. 



D 32 E - D 54 E and D 63 E - D 24 E ; 



