1899] MICROSCOPICAL JOURNAL. 279 



peroxide. With this method also a more or less intense 

 blue coloration is seen to appear on the light-colored un- 

 derground. Experience has shown me that even very old 

 blood stains and exceedingly small parts of such may be 

 identified in this manner, provided a sensible guaiacum 

 chloral solution, prepared with quite fresh resin, and at 

 the same time a liquid of Hunefeld or hydric peroxide 

 solution of right composition and controlled in regard to 

 their activity are used. A solution of Hunefeld suitable 

 for the purpose may easily be prepared, mixing f. i. 15 

 c. c. of turpentine oil, exposed to light and air for a cer- 

 tain time (but which ought not to change directly blue in 

 the guaiacum tincture), or 15 c. c. of a 3 to 5 per cent 

 hydric peroxide solution, free from acids, with 25 c. c. of 

 alcohol, 5 c. c. of chloroform and 1-5 c. c. of glacial 

 acetic acid. The zone reaction surpasses the other older 

 methods of testing by special purity of the blue color re- 

 sulting from the formation of the so-called "guaiacum 

 blue ;" besides that this purer color is more durable, ac- 

 cording to the fact that in the measure of progressive 

 mixation of the active substances of the two layers (hema- 

 tin as the oxygen-transferring body, hydric peroxide or 

 essential oil as the source of oxygen and guaiaconic acid 

 as the oxidable compound) small quantities of the intense- 

 ly blue colored oxidation product are formed gradually. 

 It is true, however, that the "guaiacum blue," especially 

 in the presence of organic reducing agents, is not very 

 stable, inasmuch as this compound, to use an expression 

 of its first investigator,' C. F. Schonbein, contains loosely 

 combined, movable and active oxygen in the ozonide state. 

 The foregoing shows, as it seems, the usefulness of the 

 modified guaiacum blood-test when cautiously applied ; 

 on the other hand, it cannot be denied that the reaction 

 is liable to certain misinterpretations,in cases where some 

 other organic or inorganic substances are present,instead 

 of blood. It is scarcely necessary to mention in this place 



