Tests ivith Preclpithis 



397 



1 in 500 })ro(lucc instant coagulation of the serum, and 1 in 1000 

 produces marked clouding. 



Detection of blood on materials not previously mentioned. 



Ten examples of wall paper of various textures and colours, red, 

 brown, yellow, blue, and green, were tested and gave typical reactions. 

 All produced neutral solutions, some of which were tinted. 



Extracts of blood dried on various kinds of paper, stones, flint, slate, 

 coal, cork, string, straw, rubber, linoleum, as well as silver and copper 

 coins, yielded satisfactory results. 



Although one piece of oak on which blood had been thickly 

 incrusted gave a marked reaction with anti-human serum, we failed to 

 obtain any reaction with blood , on two blocks of cedar and pine. The 

 quantity present on each of these was exceedingly small, and the negative 

 result was probably due to this cause. 



These experiments demonstrate that many substances in common 

 use give acid solutions. In most instances the acidity is not so marked 

 as to be of importance, but in some, unless recognised and neutralised 

 might be liable to lead to grave error. Extracts of certain substances 

 are sufficiently alkaline to impede the reaction. 



