1899] MICROSCOPICAL JOURNAL. 275 



oxygen, provided that errors are cautiously avoided by 

 check experiments. The proceeding, wanting but a short 

 explanation in reference to the more explicit description 

 in the paper quoted, chiefly consists in mixing the blood 

 solution, obtained by extraction of blood stains, with an 

 alcoholic solution of guaiacum resin (or, as it has been 

 lately proposed by 0. Dobner, with a similar but weaker 

 solution of guaiaconic acid.) It is preferable, in this case, 

 to use a solution of about 5 per cent of resin instead of 

 the alcoholic guaiacum tincture (1 to 2 per cent) mention- 

 ed by Schonbein as the common reagent, in order to se- 

 cure an easy secretion of resin in presence of small por- 

 tions of blood. In this case a milky secretion results of 

 the previously dissolved resin constituents, which, in 

 these conditions, partly attract, fix and precipitate at the 

 same time the dissolved or suspended coloring matter of 

 blood (either in the state of hemoglobin and inethemo- 

 globin or of hematin). In this way a mechanical com- 

 bination of the secreted resin with the said blood constit- 

 uents is formed, whieh process reminds us in some way of 

 the well-known method by which some ferments, lik 

 pepsin, are secreted by means of an indifferent precipi- 

 tate caused in the ferment solution and afterwards ex- 

 tracted. If, then, we separate the precipitated resin (or 

 the above-mentioned constituent acting as reagent) by 

 thoroughly dense filters (especially the newer "hardened 

 filters" of commerce), the hematin compounds are fixed 

 on the surface of the filter in extreme division together 

 with the particles of resin. These filters, when well pro- 

 tected from light and air even during the filtration pro- 

 cess and then cautiously dried in the exsiccator, may then 

 be conserved for any length of time. But a small piece 

 of them is wanted, to cause in a few moments an intense 

 blue coloration in a porcelain dish or watch glass on 

 white paper, after it has been moistened with a little 

 spirit of wine, and then a small quantity of Hunefeld's 



