1893.] MICROSCOPICAL JOUHNAL. 251 



it, over which objects are placed, wliile over the black paper, 

 etc., the object of course being on a slide 



Ranvier's One-third Alcohol.— (1 part alcohol 3()° and 2 

 parts distilled water), is a dissociation liquid of the first order. 

 Tissues rich in cells are dissociated in it in 24 hours. The fix- 

 ing and staining of the elements are then readily accom}»lished. 



Iodised Serum. — Next to dilute alcohol iodised serum is most 

 imjiortant. [This is made of the amniotic fluid of the sheep or 

 other animal and treated with iodine. It should be made in 

 large quantity in a laboratory, and is omitted here as probably 

 beyond the reach of those for whom these instructions are in- 

 tended]. 



Caustic Potassa. — In a strong solution (40 per cent), this is 

 excellent, but the preparations can not be preserved nor stained. 

 Keep the bottle corked with a rubber stopper. The solution 

 is allowed to act on the object while on the slide. To separate 

 the elements it is often only necessary to press slightly on the 

 cover glass. 



Chromic Acid. — This is used in weak solution (1 to 5,000 of 

 water). Tissues should remain in it for 2 or 3 days 



Dissociation by Partial Drying. — Place the tissue on a glass 

 plate, without liquid, and when partly dry, without being ad- 

 herent to the glass, divide it quickly with needles. If the tis- 

 sue is rich in cells, like the the marrow of bones, excellent dis- 

 sociation may be had by little blows of the side of the scalpel 

 blade. Harden by osmic acid vapor, stain by picro-carmine, 

 and mount in glycerine. An indispensable condition is to oper- 

 ate rapidly, before the drying is too far advanced. 



Dissociation in Liquid. — After a sojourn in the diluted alco- 

 hol or in iodised serum, dissociation of the tissue is easy By 

 curved scissors cut off a small piece and place it on the slide in 

 a drop of the dissociating liquid. A slight agitation by the 

 forceps will free the cells. Add a drop of picro-carmine to the 

 dilute alcohol, mixing them with a needle, and add the thin 

 cover. . . . Allow a drop of glycerine to run under. 



The following also gives good results : — Put a piece of tissue 

 in a glass tube with 10 c. c, of the i alcohol. In 24 hours, shake 

 violently, and pour out the liquid with the separated cells, and 

 add picro-carmine. Let it settle for 24 hours. When the cells 

 have fallen t6 the bottom pour off most of the fluid, draw up with 



