1899] MICROSCOPICAL JOURNAL. 381 



weakened by Jjeating to 100° C, or also by contact with 

 diluted hydrocyanic acid. In case the extract of a pre- 

 tended blood stain contains such a substance of the class 

 of ferments, instead of ingredients of blood, it will cease 

 to show the guaiacutn-reaction, even after a shorter diges- 

 tion at the temperature of the water-bath, and also a con- 

 trol-experiment with addition of hydrocyanic acid during 

 the extraction of the stain will give essentially negative 

 results. 



However, the avoiding of all possible mistakes becomes 

 rather difficult in such cases* where the presence of even 

 the smallest quantities of ferrous oxide or other ferrous 

 compounds can occur, as, for instance, in the testing of 

 suspected stains on rusty iron materials. If the rust.even 

 in the absence of blood, contains small portions of certain 

 ferrous compounds, viz., ferrous carbonate or other fer- 

 rous salts, they could, by extraction, be introduced into 

 the filtered solution, even in case the latter had not taken 

 up any ferric hydrate or basic ferric salt ; yet such an ex- 

 tract of a stain, even with the slightest trace of ferrous 

 oxide, would cause the guaiacum-blue-reaction after sub- 

 sequent addition of guaiacum resin and hydric peroxide. 

 A strict distinction of ferrous oxide and of the coloring 

 matter of blood is not very easy in such cases, because 

 the first-named compound manifests, even in the smallest 

 quantities, the same intense ''ozone-tran8ferring"power ais 

 hemoglobin or heraatin, which also contain iron. It will, 

 therefore, form the object of further experiments to find 

 out how the mentioned casual mistaking in the guaiacum- 

 blood-reaction may be eliminated. On occasion of such 

 further researches concerning the reaction discussed in 

 this paper, the question would have to be treated, whether 

 blood, which, after drying up in slow decomposition on 

 certain materials, like stone, clay or rough metallic sur- 

 faces, and after disappearance of the organic substance 

 by the action of air and water, leaves but rusty spots, 



