BLOOD AND LYMPH 267 



fluid to be tested and finally 0.4 c.c. of 3 per cent hydrogen peroxide. Note the 

 appearance of a blue color, which reaches its maximum in five to six minutes. 



The acetic acid keeps the benzidine in solution. An excess dimin- 

 ishes the delicacy of the reagent. 



Hydrogen peroxide supplies oxygen for the reaction and also bleaches 

 the blue color. An excess of peroxide interferes with the reaction by 

 destroying the catalytic power of the blood and by reacting with the 

 benzidine itself, with the formation of products which appear to have 

 an inhibitory action. It is very essential that the peroxide be added 

 last. 



The benzidine solution should be dilute. Such solutions are exceed- 

 ingly sensitive and permit the detection of blood when present in ratio 

 i : 5,000,000. 



Gregersen and Boas 1 claim that the uses"~of a too concentrated 

 benzidine solution may lead to wrong diagnosis because of the excessive 

 sensitiveness of the reagent. The feces of normal persons on a meat- 

 free diet often yield a positive reaction. They suggest the use of a 

 0.5 per cent benzidine solution and the replacement of the hydrogen 

 peroxide by barium peroxide which is much more stable. They, 

 however, admit that slight hemorrhages may go undiscovered when 

 this dilute benzidine solution is used. 



14. Hemin Test. (a) Teichmann's Method. Place a very small drop of 

 blood on a microscopic slide, add a minute gram of sodium chloride 2 and care- 

 fully evaporate to dryness over a low flame. Put a cover-glass hi place, run 

 underneath it a drop of glacial acetic acid and warm gently until the formation of 

 gas bubbles is noted. Add another drop of glacial acetic acid, cool the prepara- 

 tion, examine under the microscope and compare the crystals with those shown in 

 Figs. 84 and 85. 



The hemin crystals result from the decomposition of the hemoglobin 

 of the blood. What are the steps involved in this process? The hemin 

 crystals are also called Teichmann's crystals. Is this an absolute test 

 for blood? Is it possible to differentiate between human blood and the 

 blood of other species by means of the hemin test? 



(b) Nippe's Method. 3 Spread a small drop of blood on a slide hi the form of 

 a film and evaporate to dryness over a low flame. Now add 2 drops of a solution 

 containing o.i gram each of potassium chloride, iodide and bromide hi 100 c.c. 

 of glacial acetic acid. Place a cover-glass hi position and heat gently over a low 

 flame until gas bubbles form and the solution boils. Run 1-2 drops of the re- 

 agent underneath the cover-glass and examine under a microscope. Compare 

 the crystals with those shown hi Figs. 84 and 85. 



1 Boas: Berl. klin. Woch., 56, 939, 1919. 



2 Buckmaster considers the use of potassium chloride preferable. 



3 Nippe: Deut. med. Woch., 38, 2222, 1912. 



