254 THE AMERICAN MONTHLY [Sept., 



bones are excellent for the study ol this reaction. With the 

 point of a scalpel, remove a small quantity, spread it on a cover 

 glass, and without allowing it to dry, separate the cells by gen- 

 tle blows with the side of the blade. The cells on the plate are 

 then held over a wide mouthed bottle containing 1 or 2 c. c , of 

 osmic acid. After 10 or 15 minutes, mount in glycerine and the 

 coloring will be more conspicuous as the cells are more com- 

 pletely separated. Having become familiar with this reaction, 

 fat cells may be recognized in sections treated with this acid. 



Staining with quinoline blue is more elegant and more diffi- 

 cult. Add a few drops of a concentrated alcoholic solution to 

 a small vessel of water. Leave sections there till they are of a 

 deep blue, wash rapidly and mount in glycerine. At the end 

 of24 hours the nuclei will be decolored, the jirotoplasm a clear 

 blue, the drops of fat appearing as intensely blue granules. 

 This color selection may be immediately produced by 40 per 

 cent potash solution (Ranvier). 



This connection of fat cells with one another and with the ves- 

 sels may be well studied in the omentum of the rabbit or of a 

 kitten. . . . Inject the vessels with Prussian blue, fix the 

 omentum with a bichromate solution, remove a small piece and 

 let it partly dry as already described. Submit it to picro- 

 carmine for a few minutes, then, for at least 20 minutes, expose 

 to the osmic acid vapor. Fat is thus made insoluble, and the 

 preparation, after dehydration in alcohol and clearing by some 

 essential oil (bergamot), may be mounted in balsam. 



Another good stain for fat is made by macerating alcanet 

 root in 90° alcohol. Fix with bichromate, stain for about half 

 an hour, wash, mount in glycerine. All fat becomes red. 



TENDONS. 



For this study select the filiform tendons from the tail of a rat 

 where they form a unique bundle representing an exceedingly 

 simple tendon. They may be easily and abundantly procured 

 thus : — cut off the tail close to the body. With the fingers 

 break the end of the tail and pull it in two, thus obtaining a bun- 

 dle of filiform tendons like a skein of thread ; keep for study. 



Endothelium.— After a rapid washing, put a few oftheselittle 

 tendons, into a solution of silver nitrate, 1 part to 500 ; place 

 the vessel in the sun and keep the tendons constantly agitated. 

 When opalescent, wash in water, stain with alum carmine, wash 



