Histogenesis of the Blood Platelets. 275 



yellowish artificial light under a low magnifying power after pouring 

 back the diluted staining fluid into the wine glass. The stain is 

 to be regarded as sufficiently intense and the staining process 

 stopped by washing the preparation in water when the cytoplasm 

 of the giant cells has acquired a bright red color and the fibrils 

 of the reticulum begin to take on a red color also. If the staining 

 is found not sufficiently intense the diluted staining fluid is poured 

 back on the preparation and allowed to act longer. Over-staining 

 and the formation of a black red granular precipitate on the 

 preparation occur if the diluted staining fluid is allowed to act 

 longer than a certain time. 



2. Dehydrate in pure acetone. 



On account of the great volatility of acetone some care is 

 necessary to prevent the drying of the preparation, which should 

 be avoided. 



3. Clear in pure oil of turpentine. 



4. Mount in a thick solution of colophonium in pure oil of 

 turpentine. 



Before mounting the preparation the superfluous turpentine 

 should be carefully removed because this reagent rapidly takes 

 up water from the air and thus may cause the clouding of the prep- 

 aration or the fading of the stain. 



The solution of colophonium is made by saturating a quantity 

 of turpentine with powdered colophonium and keeping the filtered 

 solution in the paraffin embedding oven until it has evaporated 

 to the required consistence. 



The use of acetone for dehydrating and of oil of turpentine for 

 clearing and mounting is an important feature of the method, for 

 these do not destroy the characteristic staining of the granules in 

 the giant cells and platelets as do other similar reagents that I 

 have tested. 



The staining fluid is composed of a mixture of 3 parts of a solu- 

 tion of modified or polychromatized methylene blue and 10 parts 

 of a 0.2 solution of eosin, '' w.g." (Gruebler) in pure methyl alcohol. 

 It is permanent if kept in a well-stoppered bottle so that evap- 

 oration is prevented. 



