250 The Microscope. 



saturation may be speedily effected. A very sharp knife or 

 razor must be used so that no part be 'crushed in the cutting, 

 and a record made of the position and relation of each piece 

 and attached to it by a thread; it is dangerous to trust the 

 memory alone. Some excellent histologists do not cut the 

 organ into pieces, but lay it open by deep incisions. If this is 

 done they should be made as exactly as possible in the plane of 

 the desired sections, as otherwise the difficulty of obtaining this 

 and uniform sections is greatly increased. The actions of any 

 reagent may be hastened by placing the bath in a warm chani 

 ber. 



The acid or other mixture used in killing should be removed 

 as soon as possible after its action is completed, which is when 

 the specimen is perfectly saturated. 



Chromic acid and its combinations may be partly removed 

 by washing in water for from ten minutes to one hour by means 

 of the apparatus described while speaking of corrosive subli- 

 mate. After this alcohol in successively higher grades should 

 be used and this remark applies also to the final steps after 

 other fluids have been used. The author uses alcohol of 30, 50, 

 70 and 95 per cents., using 70 per cent, until the acid is entirely 

 removed from the specimens. With chromic acid this may be 

 determined by the following test: An alcoholic solution of 

 guaiacum, 1 part of the gum to 100 of alcohol, is made. If there 

 remains any chromic acid in the specimen, a few drops of the 

 alcohol last used upon it will show a blue coloration when added 

 to the above solution. This reaction is very delicate, as by it 

 one part of chromic acid to one million of solution may be 

 detected. 



GLEANINGS FROM THE JOURNAL OF THE ROYAL 

 MICROSCOPICAL SOCIETY FOR OCTOBER. 



C. H. STOWEIiL. 



KEEPING BOTH EYES OPEN IN OBSERVATION.— Mr. E. 

 M. Nelson says that the unused eye should be shut when the 

 weaker light is in the microscope, both eyes being kept open only 

 when the object is in the strongest light. By diffused daylight the 

 lfght in the instrument is the weaker, and the other eye must 



