PATHOLOGICAL T RAN SU DATES, CYSTIC FLUIDS. 67 



shake or stir thoroughly, and after twenty-four hours filter. 

 Wash the coagulum with alcohol, evaporate the filtrate to 

 dryness at a low temperature on the water-bath, dissolve the 

 residue in absolute alcohol, filter, evaporate to dryness, and 

 again dissolve the residue in absolute alcohol. If it now dis- 

 solves perfectly clear, evaporate the alcoholic solution to dry- 

 ness again ; if it does not, the treatment with absolute alcohol 

 is repeated. The residue obtained by the evaporation of the 

 alcohol is treated, after cooling, with a few drops of nitric acid, 

 and allowed to stand for twenty-four hours in the cold. 

 Usually on the addition of the nitric acid a cloudiness is first 

 formed, caused by the fatty acids, which come from the soaps 

 almost always present; gradually urea nitrate crystallizes 

 out. 



If we wish to get rid of these fatty acids, which contaminate the 

 urea nitrate, we put in the treatment with basic lead acetate. The 

 fluid obtained by concentrating the first alcoholic extract, which is 

 generally turbid, is treated with a solution of basic lead acetate, drop 

 by drop, as long as the precipitate continues perceptibly to increase, 

 and then a little ammonium carbonate solution is cautiously added. 

 The fluid above the flocculent precipitate now becomes quite clear. 

 Filter and pass a rapid stream of hydrogen sulphide into the filtrate, 

 filter again after the lead sulphide has well settled, evaporate the 

 filtrate to dryness, and dissolve the residue again in a small quantity 

 of absolute alcohol, etc. 



Examine under the microscope the urea nitrate which 

 separates (compare with Fig. 7 in the chapter on Urine, 

 page 95). Then after completely drying the crystals by 

 means of filter-paper or on a porous-clay plate and washing 

 them with some ether, dry, and heat a small quantity on 

 platinum-foil or on a crucible-cover: violent decomposition 

 or explosion. In case the amount of the urea nitrate suffices, 

 convert the remainder into urea (see chapter on Urine, page 

 95), and test this by means of its reactions. 



The amount of urea contained in pathological transudates 



