spectrum Method of Detecting Blood. 13 



The above directions apply to simple cases, where the amount 

 of material at command is amply sufficient, and the fabric on which 

 the stain is found does not contain anything that makes the blood 

 insoluble, or interferes with the various tests. I shall, however, now 

 describe what should be done in cases which are made specially 

 difficult by various causes. If the stain were very faint, from the 

 presence of very little blood, or if the greater part had been re- 

 moved by washing with water, it might be desirable not to divide 

 the material, but to examine the whole at once. The stained por- 

 tion should therefore be digested in a few drops of dilute citric acid 

 or ammonia, and the presence of haematin determined, as already 

 described. If faint and spread over a considerable surface, it might 

 be well to digest in citric acid or ammonia diluted with much more 

 water than would fill the experiment cell, and afterwards concen- 

 trate the solution by gentle evaporation. By this means blood 

 could be detected, even when considerable effort had been made to 

 remove it, and only a faint brown tinge left, just visible on white 

 linen. There would generally be no difficulty in the case of a 

 stain on cloth which had been sponged, for enough blood solution 

 would be left in the fabric. 



The presence of mordants in cloth or prints may require us to 

 somewhat modify our proceedings, especially if the stain had been 

 made wet, and to a great extent removed, so that we have only the 

 dried-up solution of blood, thoroughly incorporated with the mor- 

 dant. Certain kinds of brown cloth are of such a character, and 

 about seven years ago portions of a wetted stain were sent by me 

 to a number of the highest authorities in the detection of blood, and 

 they said that neither they nor anyone else could recognize it. 

 However, by proper care, I found that after a lapse of six years it 

 could be detected by the spectrum method. The best plan was to 

 digest a portion of the cloth in dilute ammonia, and to squeeze it 

 well over and over again, with a pair of forceps, and finally with 

 the finger and thumb, so as to obtain as much of the solution as 

 possible. This was very turbid, but when deoxidized in the usual 

 manner, and illuminated by concentrated light direct from the sun 

 itself, the band of deoxidized hsematin was quite distinct. When 

 the cell was kept for a while, so that the insoluble part settled to 

 the side, no band was visible, and therefore the haematin was evi- 

 dently combined with the mordant. It will thus be seen that it 

 may be most important not to filter or allow the insoluble matter to 

 subside, but to overcome the opacity by means of a sufficiently 

 intense light. If the sun could not be made use of, the hme or 

 electric hght would no doubt be the best substitute. 



When fresh blood solution is agitated in a test tube with vege- 

 table soil, and left until quite clear, the colouring matter is com- 

 pletely carried down with the earth. Dilute ammonia, however, 



