THE BLOOD. 121 



The same thing will occur when it is treated with nitrate 

 of silver or bichloride of mercury. 



The addition of a strong acid or alkali turns the colouring 

 matter of a brown tint. 



These results, however, are common to other mixtures of 

 animal substances in combination with colouring matter be- 

 sides the blood, and no one of them is perfectly characteristic. 



It would therefore appear, that the microscope is capable 

 of revealing evidence much more satisfactory in reference to 

 the nature of blood stains, than that which it is possible to 

 derive from chemical examination. 



Finally, it may be observed, that during the examination 

 of blood stains, other substances may be detected in con- 

 nexion with them, the presence of which would reveal not 

 merely their nature, but also the seat from which the blood 

 forming them had flowed ; thus some of the various forms of 

 epithelial cells and of hairs, may occasionally be encountered 

 in them. 



We now bring to a conclusion this long article upon the 

 grand formative fluid of the system, the blood, and pass to 

 the consideration of other fluids of the economy, viz., pus 

 and mucus. 



