OPTICAL PROPERTIES OF BLOOD. 247 



Tallquist's Chart. This consists of a small book containing blank sheets 

 of a special fine grained filter paper and a colored chart with a number of 

 shades corresponding to blood stains with different hemoglobin content. 

 To make the test a small drop of blood is drawn and placed on one of 

 the sheets of filter paper, into which it soaks and spreads. The color pro- 

 duced is compared with one of the ten shades in the color scale. 



The test is extremely simple, but its accuracy is dependent on the 

 accuracy with which the colors in the chart are printed, and their perma- 

 nence. Unfortunately the colors change as the chart, in use, is exposed to 

 light and air. 



