188 THE AMERICAN MONTHLY [June, 



following " oxygecated- water method" for getting rid of the 

 blackening caused by osmic acid treatment : 



The peroxide of hydrogen becomes reduced at contact wuth 

 organic matter, and this is bleached by the oxygen. But the 

 oxygenated water is very instable and in a short time the per- 

 oxide of hydrogen is converted into water. By the chlorine 

 method, heat was necessary and it has an injurious effect upon 

 the tissues. 



The difficulties are obviated by the peroxide of sodium 

 method. The compound is a yellowish powder ; when put in 

 water, oxygen is evolved and the liquid becomes alkaline. But 

 if the water is mixed with acid, the liquid remains neutral, be- 

 cause the soda combines with the acid. 



Large quantities of peroxide must not be put in a small 

 quantity of water, nor mineral acids be used, otherwise a 

 violent reaction is set up, oxygen being evolved in large amount 

 and the molecules of powder being thrown all around. 



The acids more convenient for use are tartaric and acetic. 

 For bleaching, use the following : Put a solution of tartaric or 

 acetic acid (10 per cent) in a vessel if for animals, and in a test 

 tube, if for microscopical sections, sink a small quantity of the 

 peroxide, add slowly 70 per cent alcohol at the surface of the 

 water, put in the object. The oxygen escapes from the water, 

 rises quickly to the level of separation of the two liquids and 

 dissolves in the alcohol, slowly bleaching the specimen which 

 is supported in the alcohol. 



MEDICAL MICROSCOPY. 



Leprosy.— In a microscopical section of a leprosy knob, two 

 sorts of bodies may be seen : 1st, round cells, having in their 

 chief mass the size of white blood corpuscles, clear and small 

 grained, not always provided with a visible nucleus ; sometimes 

 somewhat aggrandized, gulf shaped, of the character of round 

 cells, although sometimes spool-shaped and provided with pro- 

 cesses. These irregularly shaped specimens show a stronger 

 granulation. 2d, flat cells, partly in form of knolls, partly of 

 stars, which are especially distinguished from the first kind by 

 their pale clear nature and a clearly visible, oval, water-roll-like, 



