236 PHYSIOLOGICAL CHEMISTRY. 



density and width vary with the concentration. In a rela- 

 tively strong blood solution, for example, there appears to be 

 but one broad oxyhemoglobin band between D and E, but on 

 proper dilution this breaks up into two characteristic bands. 

 The question of dilution is therefore important and for any 

 given instrument and light the observer should settle this by 

 a few preliminary experiments. 



FIG. 14. Direct-vision spectroscope. 



Spectrum of Oxyhemoglobin. This consists of two 

 bands in the yellowish green portion of the spectrum between 

 D and E. The bands have not the same width, the one near 

 E being slightly broader than 'the other. The preparation of 

 proper dilutions may be illustrated in this way: 



Ex. Measure out 5 cc. of defibrinated blood and dilute it accurately 

 with 120 cc. of water. Filter into a clean flask and use the clear nitrate 

 for tests to follow. Mark this mixture Solution No. I. 



Dilute 50 cc. of No. I with 50 cc. of water and mark the mixture Solu- 

 tion No. II. 



Dilute 50 cc. of No. II with 50 cc. of water and mark the mixture Solu- 

 tion No. III. 



Dilute 50 cc. of No. Ill with 50 cc. of water and mark the mixture 

 Solution No. IV. 



Dilute 50 cc. of No. IV with 50 cc. of water and mark the mixture 

 Solution No. V. 



Dilute 50 cc. of No. V with 50 cc. of water and mark the mixture Solu- 

 tion No. VI. 



Finally, dilute 50 cc. of No. VI with 50 cc. of water and mark the 

 mixture Solution No. VII. 



We have now dilutions beginning with I in 25 and ending with I in 

 1600. The last solution is almost colorless. 



Take seven test-tubes of thin, colorless glass, and as uniform as possible 

 in diameter. Number them I to 7 and two-thirds fill each one with the 

 dilute blood solution corresponding to its mrrnber. Place each tube before 

 the narrow slit of the spectroscope and adjust the flame of an oil or gas 

 lamp so that its light may pass through the solution into the slit. Pull 



