362 VEHICLES OF CHEMICAL CORRELATION 



of these formed elements impossible. This was succeeded by the far 

 more delicate and reliable Hemin Test, which consists in placing a drop 

 of suspected fluid or saline extract of shreds of stained fabrics, upon 

 a microscope-slide, adding a crystal of salt and a drop of glacial acid, 

 heating the fluid to boiling by passing the slide to and fro over a small 

 flame, and then examining the fluid, as it cools, for hemin crystals. 

 This test may be successfully employed with samples of blood far 

 advanced in decomposition. A still more delicate test, however, is the 

 Benzidine reaction. This depends upon the power of an enzyme or 

 Peroxidase, 1 which is present in blood, to decompose Hydrogen Peroxide, 

 liberating nascent oxygen which oxidizes the benzidine with the produc- 

 tion of a green or blue color. Properly conducted, this test will detect 

 one part of blood in three hundred thousand, which means, in effect, that 

 a murderer may wash his blood-stained hands in a bath full of water, 

 and yet if any drainage remains unemptied at the bottom of the bath, 

 the fact that he has done so may be detected with certainty. Never- 

 theless even more delicate tests are available. TJius Buckmaster has 

 found that if an alcoholic solution of Guaiaconic Acid be added to blood 

 together with hydrogen peroxide, a blue color may be produced at a 

 dilution of one in five million. This test is also given by perfectly fresh 

 Milk collected and bottled with aseptic precautions, but it is not given 

 by the milk which is ordinarily obtainable in the market. 



For the identification of the Species from which blood is derived we 

 rely upon the antigenic Specificity of blood. The suspected fluid is 

 mixed with anti-human serum prepared by immunizing a rabbit 

 against human blood. The mixture is incubated, and the occurrence 

 of a flocculent precipitate indicates that the suspected fluid contained 

 either human blood or the blood of an anthropoid ape. Since "The 

 Murders in the Rue Morgue" must be admitted to have constituted 

 an entirely exceptional problem, the alternative thus presented does 

 not furnish any serious basis for uncertainty. 



THE ORIGIN AND COMPOSITION OF LYMPH. 



The tissues are not, excepting in a very few situations, bathed by 

 blood itself, but by the Lymph, which is derived from blood, and 

 through the intermediation of which the substances dissolved or 

 combined in blood are brought into physical contact with the proto- 

 plasm of the living cells. 



There was formerly much discussion of the question whether lymph 

 is elaborated from the blood by a process of active secretion, consti- 

 tuting an Exudate, or whether, on the contrary, it is a Transudate, 

 derived from the blood by passive filtration. Heidenhain believed it 

 to be an exudate for the following reasons: 



1 It is considered probable that hemoglobin itself is the agent which brings about 

 this decomposition. Catalase, which is also present in blood, decomposes hydrogen 

 peroxide with the production of inactive, or molecular oxygen. 



