in the Diagnosis of Blood Stains. 137 



with the fluids I recommend for the examination of blood stains. 

 The sHght increase of size previously mentioned as occurring in the 

 desiccation of a thin film of blood, forms, I believe, only an 

 apparent exception, and is probably due to a change of shape taking 

 place during the complete flattening out of the disks as they lose 

 their contained water. The experience of Prof. Leidy and Prof. 

 Wormley accords with mine, in that they have never seen the drying 

 or remoistening of red blood-corpnscles cause them to expand, and 

 I therefore conclude we may afiirm that when the corpuscles remain 

 uncontracted, their indications are perfectly reliable, and if they 

 shrink (as I believe they rarely do), that being the only serious 

 modification which they can undergo, the sole danger is that by a 

 possible, but not probable, mistake in diagnosis of the origin of a 

 blood stain through contraction of its corjjuscles, we might contri- 

 bute to a criminal's escape, never to the punishment of an innocent 

 party. 



But all these theoretical considerations are of very secondary 

 importance in comparison with the positive fact, as to whether 

 practically we can or cannot discriminate the stains of human blood 

 from those made by the blood of oxen and sheep, I have therefore 

 endeavoured to worh out a conclusive answer to this question, 

 obtaining it by a method which will, I trust, carry conviction to 

 the mind of every honest seeker after truth. 



On the 16th of May, 1874, my friends. Prof. J. J. Keese and 

 Dr. S. Weir Mitchell, each kindly prepared for me three packages 

 of dried blood from stains made by sprinkling the fresh fluid from 

 an ox, a man, and a sheep, upon white paper. The two series were 

 simply numbered 1, 2, and 3, and a memorandum preserved by each 

 gentleman, specifying which kind of blood composed each sample. 

 By this plan it is obvious that I was prevented from having any 

 clue to the origin of the specimens save that afibrded by the 

 microscope, and my examinations and measurements were therefore 

 entirely free from bias. 



Some small particles from specimen No. 1, handed me by Prof. 

 Eeese, were broken up into a fine dust, with a sharp knife upon a 

 slide, and covered with a film of thin glass. A few drops of the 

 ordinary three-quarter of 1 per cent, common salt solution were 

 then successively introduced at one margin of the cover, and 

 removed from the opposite edge, as they penetrated thither, by a 

 little slip of blotting-paper, thus washing away the colouring 

 matter from the tiny masses of dried clot. When these particles 

 were nearly decolourized, a drop of aniline solution was allowed 

 to flow in beneath the cover, and, after remaining about half a 

 minute, was in its turn washed away, and its place supplied by a 

 further portion of weak salt solution. 



On adjusting the specimen as thus prepared, under a ^V immer- 



L 2 



