214 Original Articles. [April, 



should first cut off a portion of the material where not marked, and 

 digest it in four or five drops of water in a watch-glass, squeezing it 

 with forceps, and moistening it over and over again. If the solution 

 became coloured, I should introduce it into a cell and determine the 

 character of the spectrum, both in its natural state, and after having 

 been acted on by the different reagents already mentioned. I should 

 then add a very little blood to a few drops of water, and digest in that 

 solution a small piece of the material, so as to make out whether it 

 contained anything that acts on the colouring matter of blood. Having 

 satisfied myself on these points, I should cut off a small bit of the 

 stained portion, using from roth to ith of an inch square, according to 

 the character of the mark, and the amount of material at my disposal, 

 and digest it in three or four drops of water in a watch-glass. If the 

 solution became well coloured, I should not squeeze the material so 

 much as to detach many minute particles of foreign matter ; but if 

 there appeared to be very little colour present, I should dissolve from 

 it all I could, and take care to waste as little solution as possible, and 

 have no more than would properly fill the cell. Transferring the 

 solution to a cell about £ inch long and |th inch in diameter, and 

 having placed it horizontally in front of the slit, and left it a 

 short time, so that the minute particles of foreign matter might settle 

 to the lower side of the tube, I should examine the spectrum, and 

 carefully note the exact position and general characters of the absorp- 

 tion-bands, if the solution were too strong, diluting it until they were 

 well seen. If the spectrum were like No. 2, I should feel nearly sure 

 that the mark was due to blood ; and, if it had been kept dry in a 

 town, I should also conclude that it was nearly fresh. If it were as 

 No. 4, I should feel inclined to believe that it had been exposed to 

 the air for some time ; but, unfortunately, the character of the atmo- 

 sphere makes so much difference that no rule can be given. If, how- 

 ever, in any particular instance a knowledge of the length of time 

 that had elapsed since the blood was fresh were of importance, a more 

 definite opinion might be formed after a few days' experiment with 

 fresh blood, keeping it, if possible, under the same conditions, and 

 using the same material as in the case in question. If the spectrum 

 obtained was like No. 4, I should add ammonia in excess, so as to 

 obtain one like No. 5, and afterwards add citric acid in excess, so as 

 to see spectrum No. 7. Then adding excess of ammonia and a small 

 quantity of protosulphate of iron, stirring it to dissolve all the oxide, 

 but not so much as to peroxidize and make the solution so yellow that 

 it would not transmit the green, the spectrum No. 8 would be well 

 seen, even when a very small quantity of blood had been present. If 

 plenty of material remained, I should take another portion, dissolve 

 the blood from it, add citrate of ammonia, taking great care that the 

 solution was never acid, and then deoxidize by means of a little proto- 

 sulphate of iron, so as to obtain No. 6 ; and I should also mount a 

 dry specimen on glass, to keep as a permanent proof. If all the 

 characteristic results followed, I think no one could hesitate in giving 

 evidence that the mark was blood ; though, of course, these facts alone 

 would not decide whether or not it was human — if possible, that must 



