STAINING FLUIDS. 21 



TJie Vincent microtome. This instrument, which was de- 

 vised by Dr. Vincent, of New York city, is a flat piece of steel 

 (Fig. 12) 12 inches long by 2 2 inches wide, with a bevelled 

 cutting edge, 6 inches long. The handle is simply the rounded 

 and smoothed extremity of the knife. 



It has been in use at the School of Histology connected with 

 the Columbia Veterinary College, and has proved to be a very 

 efficient knife. 



The mode of action is very simple. The object having been 

 previously placed in any ordinary hand-cylinder and mounted 



in wax, paraffine, or pith, the sections are made by a stroke of 

 the knife, which is pushed straight forward. As will be readily 

 seen, the larger the section the wider the knife must be. 



The blade is made of the best plate steel, and is easily kept 

 in order. 



STAINING FLUIDS. 



Ammonia carmine. This is one of the oldest and best 

 known solutions. Take one part, by weight, of the best car- 

 mine, which is known as " No. 40," dissolve it in 100 parts of 

 distilled water, and add one part of aqua ammonise. The pre- 

 vious dull color now gives place to a most brilliant and deep 

 red. It is necessary, however, that the carmine be either neu- 

 tral or very faintly alkaline, else the color will diffuse and the 

 tissues will not be differentiated. Expose the fluid, therefore, 

 for some weeks to the air, or evaporate over the water-bath 

 until the odor of ammonia is no longer perceptible. 



The nuclei should be deeply and brightly stained, while the 

 intercellular substance is in no way affected. If, however, 

 diffusion has taken place, a great deal of it may be removed 

 by soaking the section in a saturated alcoholic solution of ox- 

 alic acid. When a brick-red color has in this way been ob- 

 tained, the object has been accomplished. Crystals of oxalic 

 acid are apt to be found in specimens that have been prepared 



