244 



PHYSIOLOGICAL CHEMISTRY. 



The absorption ratios for a number of physiologically important sub- 

 stances are shown in the above table. The spectral regions are given 

 in the usual wave lengths. 



CLINICAL METHODS OF ESTIMATING OXYHEMOGLOBIN. 



The spectrophotometric estimation of oxyhemoglobin as 

 described above is not simple enough for quick clinical deter- 

 minations, which have to be made in the course of daily prac- 

 tice by medical men. Other forms of apparatus have been 

 devised for this purpose and are in common use. In all of 

 these, comparison is made between the blood under examina- 

 tion, properly diluted, and a standard color assumed to repre- 

 sent normal blood correspondingly diluted. Some of these 

 appliances give pretty good results, but others are very faulty 

 and the values they furnish quite untrustworthy. In the fol- 

 lowing pages several of the commoner forms will be briefly 

 described. 



Fleischl's Hemometer. This instrument consists essentially of a circular 

 cell with glass bottom divided by a vertical partition into two equal com- 

 partments as shown below. In one of these the accurately diluted blood 



is placed in given volume. The 

 other compartment is filled with pure 

 water to the same level. The cell 

 rests on a stage below which there 

 is mounted a white reflecting mirror 

 by means of which light may be 

 thrown upward to illuminate the two 

 compartments of the cell uniformly. 

 Immediately under the water com- 

 partment a long colored glass wedge 

 is placed in such a manner that light 

 must pass through it into the water. 

 By a rack and pinion mechanism this 

 wedge may be moved to the right or 

 left under the water cell so as to 

 bring a thinner or thicker portion 

 of the glass below the water. The 

 glass is colored by means of purple 

 of Cassius to resemble diluted blood 



as nearly as possible, and the light shining through it into the water im- 

 parts a more or less perfect blood color to it. The wedge is moved 



FIG. 20. Fleischl hemometer, 

 showing divided cell for blood and 

 water and reflecting mirror to 

 secure uniform illumination. 



