1899] MICROSCOPICAL JOURNAL. 277 



many years old may, by this operation — after a some- 

 what longer contact with the solution — be removed to 

 such a degree that their trace is but hardly discernible on 

 the linen. It may be observed on this occasion that the 

 solution of the blood constituents by aqueous chloral hy- 

 drate is much facilitated if the blood spots have been 

 previously wetted with small quantities of concentrated 

 acetic acid. The use of this acid is not only admissible 

 for itself, as the guaiacum-blue is not affected by it, but 

 even offers a certain advantage concerning a reaction of 

 control to be mentioned later on. 



Inasmuch as guaiacum resin, as well as the guaiaconic 

 acid, specially concerned in the formation of "guaiacum 

 blue," are both easily soluble in the concentrated chloral 

 hydrate solution, a simple method may be devised for the 

 extraction of blood stains and the subsequent detection 

 of the coloring matter of blood. 



In fact, the guaiacum blood test can be prepared and 

 managed on the simplest terms in this way, that first the 

 colored spots in question, after moistening with a little 

 acetic acid, are extracted either with a 70 per cent chlo- 

 ral hydrate solution or directly with a 1 per cent solution 

 of guaiacum in aqueous chloral hydrate, containing 70 to 

 75 per cent of the latter. In regard to the fact that the 

 resin constituents concerned in the subsequent reaction 

 show a marked tendency for spontaneous oxidation — as 

 is sufficiently proved by the well-known change of color 

 in the air and light — this latter method, on the whole, 

 seems less preferable than the first named, which con- 

 sists in first extracting the blood by means of chloral solu- 

 tion and then adding to the resulting blood solution about 

 an equal volume of the guaiacum chloral solution. If in 

 this process the blood stain has been moistened with 

 acetic acid previous to the treatment with chloral hydrate, 

 the addition of guaiacum chloral solution to the chloralic 

 extract of the stain to be tested for blood will permit a 



