1893.] MICROSCOPICAL JOURNAL. 77 



flatten them by compressing them in the fingers. Lower the piston 

 of the microtome until there is room enough to receive the speci- 

 men, which is solidly wedged in by the compressed pith, and in- 

 vert the microtome in a vessel of alcohol. The swelling of the 

 pith fastens it more firmly in place. 



The preparation, arranged in the microtome, is raised by the 

 screw till level with the platform, then more or less above. After 

 leveling the surface by cutting ofl' the projecting irregularities, if 

 the screw is moved a fifth, a fourth, a third of a turn, we can with 

 a razor, one face exactly applied to the platform, cut very thin 

 sections. As in free-hand sectioning, it is necessary that the razor 

 and the tissue be covered w^ith alcohol. This is easily done by 

 dipping the microtome and the razor after each cut into a saucer 

 of alcohol. Ranvier's microtome is a valuable instrument to the 

 histologist, and should be procured when he buys his microscope. 

 It is specially useful for section-cutting with gum imbedding, but 

 to obtain good results the tissue should be saturated and well hard- 

 ened. . . . 



Staining. 



Sections .... should be prepared for staining by methods dif- 

 fering according to the imbedding material. 



1. When simply hardened by alcohol, picric acid, the bichro- 

 mates, or imbedded in gum, the sections are placed at once into a 

 basin of water. They are left there for a certain time, when 

 they are ready for staining. When fixed by picric acid, the 

 yellow color must be removed ; when infiltrated by gum, color- 

 ing agents should be used only after itsentire removal. 



2. Sections cut in celloidin should be placed in alcohol, then on 

 the slide and treated difterently, according as to whether they are 

 to be stained by an acoholic or an aqueous solution. In the 

 former they are treated by a series of alcohols more and more 

 diluted (alcohol S20, and at ^), finally by water and by the stain. 

 In the second case the section is stained immediatelv after leaving 

 the alcohol. Sections in celloidin should be stained without re- 

 moving the iinbedding material. With paraffin sections all the 

 paraffin should be first removed. The section is spread on the 

 slide by a dry brush, and benzine added till all traces of the paraf- 

 fin have disappeared ; let the excess of benzine run oft and sub- 

 stitute absolute alcohol. We then proceed as for celloidin sections 

 .... The histological student should by all means procure the 

 following stains from among the great number used : ammoniated 

 picro-carmine, alum carmine, hiematoxylin and a few aniline 

 colors. 



To stain sections with picro-carmine. — This may be used 

 after any fixing reagent ; but it is after alcohol and imbedding 

 in gum that the best results are obtained. By needles place the 

 section on the slide ; sponge oft' the excess of water by bibulous 

 paper ; let fall a drop of the picro-carmine on the section. Ex- 

 amine with a low power, and when the stain is deep enough add 



