222 Scientific Proceedings, Royal Dublin Society. 



benzidine-paper as a test for blood in clinical work. He uses strips of filter- 

 paper that have been soaked in the acetic solution of benzidine and dried. 

 The slip is moistened with the fluid to be tested, and a few drops of 

 hydrogen peroxide di'opped on. I have not as yet enough experience of this 

 method to enable me to speak with certainty as to its merits. But such 

 experiments as I have tried — about a dozen — with benzidine-paper have not 

 been encouraging. I find that when H2O2, is dropped on to benzidine paper, 

 without addition of any suspected fluid, greenish to bluish tinges make their 

 appearance quite regularly as the paper dries, and give rise to doubt. 

 Whatever be the value of the method for clinical purposes, I consider that 

 for medico-legal work it is far inferior to the direct use of solution in 

 ordinary or capillary tubes. Eiiihorn records an observation which I 

 thought it well to repeat. In testing the efi'ect of various food-stuffs on 

 benzidine he observed that porridge {Griitze) boiled with water or milk 

 at once yielded the blue reaction with benzidine-paper. I have tried the 

 effect of porridge made with " flake oatmeal " on the benzidine reagent in 

 test-tubes, both with and without milk, and have obtained a practically 

 negative result. 



Another method of using benzidine is in alcoholic solution. This is the 

 way recommended by Ascarelli of the Institute for Legal Medicine at 

 Rome (7). He mixes about 2 c.c. of the saturated solution in absolute 

 alcohol and H2O2, and adds a few drops of glacial acetic acid. With this 

 reagent he obtains reliable positive results with blood-solutions as weak as 

 1 : 250,000. I can only say that my experience of alcoholic solutions of 

 benzidine has not been satisfactory. In my hands they have proved capricious 

 and occasionally insensitive. 



An objection urged against the test by Schumm (8) is that samples or the 

 substance obtained from the most reliable sources vary considerably in their 

 delicacy. Of fourteen samples obtained from Merck he found that three 

 were sensitive up to 1 : 200,000, whilst two did not reach beyond 1 : 50,000, 

 and nine gave only a dirty red coloration with 1 : 10,000. Of two pre- 

 parations from Kahlbaum one was sensitive up to 1 : 2,000,000 (!), the other 

 to 50,000. 



My own experience on this point is limited to tliree preparations, two 

 from Merck and one from Kahlbaum. I found that one from the first- 

 named source was very sensitive at first; but after standing in a corked bottle 

 in the laboratory for over a year it liad turned a faint pink, and was insensitive 

 at 1 : 10,000. The other Merck preparation was, when fresh, sensitive up to 

 1 : 50,000, not beyond. The Kahlbaum product reacted up to 1 : 500,000 

 (controlled by addition of pure water to the other half of the test-solution). 



