1889.] MICKOSCOPICAL JOUKNAL. 219 



animal. A new-born rat is killed by breaking up the medulla, and 

 thin pieces of the mucoid connective tissue are removed and spread out 

 in a thin layer on a slide, a few drops of normal salt solution added, 

 and then covered. 



Permanent preparations of the placques may be made as follows : 

 A thin layer of blood is spread quickly on a cover-glass, which is then 

 dropped in a one per cent, solution of osmic acid. Kemp places a drop 

 of blood on a cover-glass, moves it about rapidly, and then washes off 

 the blood with salt solution. The placques adhere to the cover, the 

 cells being washed away. The cover is then placed in a 1% solution 

 of osmic acid. After the covers have been removed from the osmic 

 acid they are allowed to dry in the air, and then mounted by inverting 

 them on a drop of balsam on a slide. For staining the placques, dilute 

 solutions of methyl-violet, gentian-violet, or fuchsin may be used. On 

 a cover-glass preparation are placed a few drops of the staining solu- 

 tion, which is allowed to remain for 2 to 5 minutes, then it is gently 

 washed off with distilled water. The cover is then dried and mounted 

 as above. The placques, as well as the white cells, are stained. 



Fibrin. — A large drop of blood is placed on a slide and covered. It 

 is then placed under a bell-jar with a dish of water, thus forming a moist 

 chamber. At the end of an hour the slide is removed and placed in a 

 dish of water ; the cover-glass is carefully removed under water, taking 

 care not to disturb the film of blood. The slide is allowed to remain 

 in the water for several minutes until the coloring matter is dissolved 

 out. Then remove the slide, absorb the surplus water with filter-paper, 

 taking care not to disturb the film of fibrin. Then add a few drops of 

 fuschin [sat. alcoholic sol. of fuschin 1 part, alcohol 3 parts, water 10 

 parts], and put on a cover-glass. This fluid stains red the filaments 

 of fibrin and the nuclei of any of the white cells that may remain in the 

 clot, at the same time rendering any of the red cells colorless. This 

 preparation cannot be preserved permanently. 



Blood Crystals. — Haemoglobin crystallizes very slowly from human 

 blood, while in some of the lower animals, especially the rodents, the 

 crystals form rapidly. 



Hoppe-Seyler recommends the following process for obtaining 

 haemoglobin crystals from blood : Defibrinated blood is mixed with 10 

 volumes of a 10 per cent, solution of sodium chloride and allowed to 

 stand two days. Then the upper layer of fluid is drawn off with a 

 pipette and the thick layer of cells washed by decantation. They are 

 then shaken up with an equal volume of ether, which dissolves the 

 cells. The ether is then removed and the lake-colored fluid filtered. 

 The filtrate is shaken up with \ its volume of alcohol at o° C, and the 

 mixture allowed to stand two to three days in the cold, when numerous 

 crystals of haemoglobin will have separated ; these are filtered out, dried 

 between filter-paper, and mounted in thick balsam. 



Von Stein places a thin layer of defibrinated blood on a slide, and 

 when it begins to dry at the edges covers it with a drop of thick balsam. 

 As long as the odor of balsam remains the preparation remains uncov- 

 ered ; when this has disappeared the balsam is removed with a knife, 

 wet with ether, turpentine, or oil of cloves ; a cover-glass is then put 

 on, and a ring of balsam or asphalt painted around its edge. Von 

 Stein has kept slides prepared in this manner for ten years. 



